MCP7940N Datasheet by Microchip Technology

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2011-2018 Microchip Technology Inc. DS20005010G-page 1
MCP7940N
Timekeeping Features
Real-Time Clock/Calendar (RTCC):
- Hours, Minutes, Seconds, Day of Week, Day,
Month, Year
- Leap year compensated to 2399
- 12/24 hour modes
Oscillator for 32.768 kHz Crystals:
- Optimized for 6-9 pF crystals
On-Chip Digital Trimming/Calibration:
- ±1 PPM resolution
- ±129 PPM range
Dual Programmable Alarms
Versatile Output Pin:
- Clock output with selectable frequency
- Alarm output
- General purpose output
Power-Fail Time-Stamp:
- Time logged on switchover to and from
Battery mode
Low-Power Features
Wide Voltage Range:
- Operating voltage range of 1.8V to 5.5V
- Backup voltage range of 1.3V to 5.5V
Low Typical Timekeeping Current:
- Operating from VCC: 1.2 μA at 3.3V
- Operating from battery backup: 925 nA at
3.0V
Automatic Switchover to Battery Backup
User Memory
64-byte Battery-Backed SRAM
Operating Ranges
2-Wire Serial Interface, I2C Compatible
-I
2C clock rate up to 400 kHz
Temperature Range:
- Industrial (I): -40°C to +85°C
- Extended (E): -40°C to +125°C
Packages
8-Lead SOIC, MSOP, TSSOP, PDIP and 2x3
TDFN
General Description
The MCP7940N Real-Time Clock/Calendar (RTCC)
tracks time using internal counters for hours, minutes,
seconds, days, months, years, and day of week.
Alarms can be configured on all counters up to and
including months. For usage and configuration, the
MCP7940N supports I2C communications up to 400
kHz.
The open-drain, multi-functional output can be
configured to assert on an alarm match, to output a
selectable frequency square wave, or as a general
purpose output.
The MCP7940N is designed to operate using a 32.768
kHz tuning fork crystal with external crystal load
capacitors. On-chip digital trimming can be used to
adjust for frequency variance caused by crystal
tolerance and temperature.
SRAM and timekeeping circuitry are powered from the
back-up supply when main power is lost, allowing the
device to maintain accurate time and the SRAM
contents. The times when the device switches over to
the back-up supply and when primary power returns
are both logged by the power-fail time-stamp.
Package Types
SOIC, MSOP, TSSOP(1), PDIP(1)
X1
X2
V
BAT
VSS
1
2
3
4
8
7
6
5
VCC
MFP
SCL
SDA
TDFN(1)
X1
X2
VSS
MFP
SDA
VCC8
7
5
1
2
4
VBAT 3 SCL6
Note 1: Available in I-temp only.
Battery-Backed I2C Real-Time Clock/Calendar with SRAM
FIGURE 1-2: BLOCK DIAGRAM © 2011-2013 Mlcrucmp Technology Inc
2011-2018 Microchip Technology Inc. DS20005010G-page 2
MCP7940N
FIGURE 1-1: TYPICAL APPLICATION SCHEMATIC
FIGURE 1-2: BLOCK DIAGRAM
VCC VCCVCC
VBAT
CX1
32.768 KHZ
CX2
VBAT
X2
X1
SCL
SDA
MFP
VSS
VCC
1
2
3
4
5
7
6
8
PIC® MCU MCP7940N
32.768 kHz
I2C Interface
and Addressing
Control Logic
SRAM
Clock Divider
Digital Trimming
Square Wave
Output Alarms
Output Logic
Seconds
Minutes
Hours
Day of Week
Date
Month
Year
Configuration
Oscillator
X1
X2
SCL
SDA
MFP
Power Control
and Switchover
VCC
VBAT
Power-Fail
Time-Stamp
VSS
2011-2018 Microchip Technology Inc. DS20005010G-page 3
MCP7940N
1.0 ELECTRICAL CHARACTERISTICS
Absolute Maximum Ratings (†)
VCC.............................................................................................................................................................................6.5V
All inputs and outputs (except SDA and SCL) w.r.t. VSS .................................................................... -0.6V to VCC +1.0V
SDA and SCL w.r.t. VSS ............................................................................................................................... -0.6V to 6.5V
Storage temperature ...............................................................................................................................-65°C to +150°C
Ambient temperature with power applied ................................................................................................-40°C to +125°C
ESD protection on all pins   4 kV
TABLE 1-1: DC CHARACTERISTICS
NOTICE: Stresses above those listed under “Absolute Maximum Ratings” may cause permanent damage to the
device. This is a stress rating only and functional operation of the device at those or any other conditions above those
indicated in the operational listings of this specification is not implied. Exposure to maximum rating conditions for
extended periods may affect device reliability.
DC CHARACTERISTICS
Electrical Characteristics:
Industrial (I): VCC = +1.8V to 5.5V TA = -40°C to +85°C
Extended (E): VCC = +1.8V to 5.5V TA = -40°C to +125°C
Param.
No. Sym. Characteristic Min. Typ.(2) Max. Units Conditions
D1 VIH High-level input voltage 0.7 VCC —— V
D2 VIL Low-level input voltage 0.3 VCC
0.2 VCC
V
V
VCC 2.5V
VCC < 2.5V
D3 VHYS Hysteresis of Schmitt
Trigger inputs
(SDA, SCL pins)
0.05
VCC
—— V(Note 1)
D4 VOL Low-level output voltage
(MFP, SDA pins)
0.40 V IOL = 3.0 mA @ VCC = 4.5V
IOL = 2.1 mA @ VCC = 2.5V
D5 ILI Input leakage current ±1 AVIN = VSS or VCC
D6 ILO Output leakage current ±1 AVOUT = VSS or VCC
D7 CIN,
COUT
Pin capacitance
(SDA, SCL, MFP pins)
10 pF VCC = 5.0V (Note 1)
TA = 25°C, f = 1 MHz
D8 COSC Oscillator pin
capacitance (X1, X2 pins)
—3pF(Note 1)
D9 ICCREAD SRAM/RTCC register
operating current
300 AVCC = 5.5V, SCL = 400 kHz
ICCWRITE 400 AVCC = 5.5V, SCL = 400 kHz
D10 ICCDAT VCC data-retention
current (oscillator off)
——1A SCL, SDA, VCC = 5.5V (I-Temp)
——5A SCL, SDA, VCC = 5.5V (E-temp)
D11 ICCT Timekeeping current 1.2 AVCC = 3.3V (Note 1)
D12 VTRIP Power-fail switchover
voltage
1.3 1.5 1.7 V —
D13 VBAT Backup supply voltage
range
1.3 5.5 V (Note 1)
D14 IBATT Timekeeping backup
current
——
925
850
1200
9000
nA
nA
nA
VBAT = 1.3V, VCC = VSS (Note 1)
VBAT = 3.0V, VCC = VSS (Note 1)
VBAT = 5.5V, VCC = VSS (Note 1)
Note 1: This parameter is not tested but ensured by characterization.
2: Typical measurements taken at room temperature.
2011-2018 Microchip Technology Inc. DS20005010G-page 4
MCP7940N
D15 IBATDAT VBAT data retention
current (oscillator off)
750 nA VBAT = 3.6V, VCC = VSS
DC CHARACTERISTICS (Continued)
Electrical Characteristics:
Industrial (I): VCC = +1.8V to 5.5V TA = -40°C to +85°C
Extended (E): VCC = +1.8V to 5.5V TA = -40°C to +125°C
Param.
No. Sym. Characteristic Min. Typ.(2) Max. Units Conditions
Note 1: This parameter is not tested but ensured by characterization.
2: Typical measurements taken at room temperature.
2011-2018 Microchip Technology Inc. DS20005010G-page 5
MCP7940N
TABLE 1-2: AC CHARACTERISTICS
AC CHARACTERISTICS
Electrical Characteristics:
Industrial (I): VCC = +1.8V to 5.5V TA = -40°C to +85°C
Extended (E): VCC = +1.8V to 5.5V TA = -40°C to +125°C
Param.
No. Symbol Characteristic Min. Typ. Max. Units Conditions
1F
CLK Clock frequency
100
400
kHz 1.8V VCC < 2.5V
2.5V VCC 5.5V
2T
HIGH Clock high time 4000
600
ns 1.8V VCC < 2.5V
2.5V VCC 5.5V
3T
LOW Clock low time 4700
1300
ns 1.8V VCC < 2.5V
2.5V VCC 5.5V
4T
RSDA and SCL rise time
(Note 1)
1000
300
ns 1.8V VCC < 2.5V
2.5V VCC 5.5V
5T
FSDA and SCL fall time
(Note 1)
1000
300
ns 1.8V VCC < 2.5V
2.5V VCC 5.5V
6T
HD:STA Start condition hold time 4000
600
ns 1.8V VCC < 2.5V
2.5V VCC 5.5V
7T
SU:STA Start condition setup time 4700
600
ns 1.8V VCC < 2.5V
2.5V VCC 5.5V
8T
HD:DAT Data input hold time 0 ns (Note 2)
9T
SU:DAT Data input setup time 250
100
ns 1.8V VCC < 2.5V
2.5V VCC 5.5V
10 TSU:STO Stop condition setup time 4000
600
ns 1.8V VCC < 2.5V
2.5V VCC 5.5V
11 TAA Output valid from clock
3500
900
ns 1.8V VCC < 2.5V
2.5V VCC 5.5V
12 TBUF Bus free time: Time the bus
must be free before a new
transmission can start
4700
1300
ns 1.8V VCC < 2.5V
2.5V VCC 5.5V
13 TSP Input filter spike suppression
(SDA and SCL pins)
50 ns (Note 1)
14 TFVCC VCC fall time 300 s(Note 1)
15 TRVCC VCC rise time 0 s(Note 1)
16 FOSC Oscillator frequency 32.768 kHz
17 TOSF Oscillator timeout period 1 ms (Note 1)
Note 1: Not 100% tested.
2: As a transmitter, the device must provide an internal minimum delay time to bridge the undefined region
(minimum 300 ns) of the falling edge of SCL to avoid unintended generation of Start or Stop conditions.
2011-2018 Microchip Technology Inc. DS20005010G-page 6
MCP7940N
FIGURE 1-3: I2C BUS TIMING DATA
FIGURE 1-4: POWER SUPPLY TRANSITION TIMING
SCL
SDA
In
SDA
Out
5
7
6
13
3
2
89
11
D3 4
10
12
VCC
VTRIP(MAX)
VTRIP(MIN)
14 15
2011-2018 Microchip Technology Inc. DS20005010G-page 7
MCP7940N
2.0 TYPICAL PERFORMANCE CURVE
FIGURE 2-1: TIMEKEEPING BACKUP
CURRENT VS. BACKUP
SUPPLY VOLTAGE
Note: The graphs and tables provided following this note are a statistical summary based on a limited number of
samples and are provided for informational purposes only. The performance characteristics listed herein
are not tested or guaranteed. In some graphs or tables, the data represented may be outside the specified
operating range (e.g., outside specified power supply range) and therefore, outside the warranted range.
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
1.30 1.90 2.50 3.10 3.70 4.30 4.90
5.50
I
BATT
Current (µA)
V
BAT
Voltage (V)
-40
25
85
TA = 25°C
Quanz Crysml Input Exmrnal Oscillamr Inpul
2011-2018 Microchip Technology Inc. DS20005010G-page 8
MCP7940N
3.0 PIN DESCRIPTIONS
The descriptions of the pins are listed in Table 3-1.
TABLE 3-1: PIN FUNCTION TABLE
3.1 Serial Data (SDA)
This is a bidirectional pin used to transfer addresses
and data into and out of the device. It is an open-drain
terminal. Therefore, the SDA bus requires a pull-up
resistor to VCC (typically 10 k for 100 kHz, 2 k for
400 kHz). For normal data transfer, SDA is allowed to
change only during SCL low. Changes during SCL high
are reserved for indicating the Start and Stop
conditions.
3.2 Serial Clock (SCL)
This input is used to synchronize the data transfer to
and from the device.
3.3 Oscillator Input/Output (X1, X2)
These pins are used as the connections for an external
32.768 kHz quartz crystal and load capacitors. X1 is
the crystal oscillator input and X2 is the output. The
MCP7940N is designed to allow for the use of external
load capacitors in order to provide additional flexibility
when choosing external crystals. The MCP7940N is
optimized for crystals with a specified load capacitance
of 6-9 pF.
X1 also serves as the external clock input when the
MCP7940N is configured to use an external oscillator.
3.4 Multifunction Pin (MFP)
This is an output pin used for the alarm and square
wave output functions. It can also serve as a general
purpose output pin by controlling the OUT bit in the
CONTROL register.
The MFP is an open-drain output and requires a pull-up
resistor to Vcc (typically 10 k). This pin may be left
floating if not used.
3.5 Backup Supply (VBAT)
This is the input for a backup supply to maintain the
RTCC and SRAM registers during the time when VCC
is unavailable.
If the battery backup feature is not being used, the
VBAT pin should be connected to VSS.
Name 8-pin
SOIC
8-pin
MSOP
8-pin
TSSOP
8-pin
TDFN
8-pin
PDIP Function
X1 11111Quartz Crystal Input, External Oscillator Input
X2 22222Quartz Crystal Output
VBAT 33333Battery Backup Supply Input
Vss 44444Ground
SDA 55555Bidirectional Serial Data (I2C)
SCL 66666Serial Clock (I2C)
MFP 77777Multifunction Pin
Vcc 88888Primary Power Supply
Note: Exposed pad on TFDN can be connected to Vss or left floating.
2011-2018 Microchip Technology Inc. DS20005010G-page 9
MCP7940N
4.0 I2C BUS CHARACTERISTICS
4.1 I2C Interface
The MCP7940N supports a bidirectional 2-wire bus
and data transmission protocol. A device that sends
data onto the bus is defined as transmitter, and a
device receiving data as receiver. The bus has to be
controlled by a master device which generates the
Start and Stop conditions, while the MCP7940N works
as slave. Both master and slave can operate as
transmitter or receiver but the master device
determines which mode is activated.
4.1.1 BUS CHARACTERISTICS
The following bus protocol has been defined:
Data transfer may be initiated only when the bus
is not busy.
During data transfer, the data line must remain
stable whenever the clock line is high. Changes in
the data line while the clock line is high will be
interpreted as a Start or Stop condition.
Accordingly, the following bus conditions have been
defined (Figure 4-1).
4.1.1.1 Bus Not Busy (A)
Both data and clock lines remain high.
4.1.1.2 Start Data Transfer (B)
A high-to-low transition of the SDA line while the clock
(SCL) is high determines a Start condition. All
commands must be preceded by a Start condition.
4.1.1.3 Stop Data Transfer (C)
A low-to-high transition of the SDA line while the clock
(SCL) is high determines a Stop condition. All
operations must end with a Stop condition.
4.1.1.4 Data Valid (D)
The state of the data line represents valid data when,
after a Start condition, the data line is stable for the
duration of the high period of the clock signal.
The data on the line must be changed during the low
period of the clock signal. There is one bit of data per
clock pulse.
Each data transfer is initiated with a Start condition and
terminated with a Stop condition. The number of the
data bytes transferred between the Start and Stop
conditions is determined by the master device.
4.1.1.5 Acknowledge
Each receiving device, when addressed, is obliged to
generate an Acknowledge signal after the reception of
each byte. The master device must generate an extra
clock pulse which is associated with this Acknowledge
bit.
A device that acknowledges must pull down the SDA
line during the Acknowledge clock pulse in such a way
that the SDA line is stable-low during the high period of
the Acknowledge-related clock pulse. Of course, setup
and hold times must be taken into account. During
reads, a master must signal an end of data to the slave
by NOT generating an Acknowledge bit on the last byte
that has been clocked out of the slave. In this case, the
slave (MCP7940N) will leave the data line high to
enable the master to generate the Stop condition.
FIGURE 4-1: DATA TRANSFER SEQUENCE ON THE SERIAL BUS
Note: The I2C interface is disabled while operat-
ing from the backup power supply.
Address or
Acknowledge
Valid
Data
Allowed
to Change
Stop
Condition
Start
Condition
SCL
SDA
(A) (B) (D) (D) (C) (A)
2011-2018 Microchip Technology Inc. DS20005010G-page 10
MCP7940N
FIGURE 4-2: ACKNOWLEDGE TIMING
4.1.2 DEVICE ADDRESSING
The control byte is the first byte received following the
Start condition from the master device (Figure 4-3).
The control byte begins with a 4-bit control code. For
the MCP7940N, this is set ‘1101’ for register read and
write operations. The next three bits are non-config-
urable Chip Select bits that must always be set to ‘1’.
The last bit of the control byte defines the operation to
be performed. When set to a ‘1’ a read operation is
selected, and when set to a ‘0’ a write operation is
selected.
The combination of the 4-bit control code and the three
Chip Select bits is called the slave address. Upon
receiving a valid slave address, the slave device out-
puts an acknowledge signal on the SDA line. Depend-
ing on the state of the R/W bit, the MCP7940N will
select a read or a write operation.
FIGURE 4-3: CONTROL BYTE FORMAT
SCL 987654321123
Transmitter must release the SDA line at this point
allowing the Receiver to pull the SDA line low to
acknowledge the previous eight bits of data.
Receiver must release the SDA line at this point
so the Transmitter can continue sending data.
Data from transmitter Data from transmitter
SDA
Acknowledge
Bit
1101111S ACKR/W
Control Code
Chip Select
Bits
Acknowledge Bit
Start Bit
Read/Write Bit
RTCC Register/SRAM Control Byte
2011-2018 Microchip Technology Inc. DS20005010G-page 11
MCP7940N
5.0 FUNCTIONAL DESCRIPTION
The MCP7940N is a highly-integrated Real-Time
Clock/Calendar (RTCC). Using an on-board, low-
power oscillator, the current time is maintained in sec-
onds, minutes, hours, day of week, date, month, and
year. The MCP7940N also features 64 bytes of general
purpose SRAM. Two alarm modules allow interrupts to
be generated at specific times with flexible comparison
options. Digital trimming can be used to compensate
for inaccuracies inherent with crystals. Using the
backup supply input and an integrated power switch,
the MCP7940N will automatically switch to backup
power when primary power is unavailable, allowing the
current time and the SRAM contents to be maintained.
The time-stamp module captures the time when pri-
mary power is lost and when it is restored.
The RTCC configuration and Status registers are used
to access all of the modules featured on the
MCP7940N.
5.1 Memory Organization
The MCP7940N features two different blocks of mem-
ory: the RTCC registers and general purpose SRAM
(Figure 5-1). They share the same address space,
accessed through the ‘1101111X’ control byte.
Unused locations are not accessible. The MCP7940N
will not acknowledge if the address is out of range, as
shown in the shaded region of the memory map in
Figure 5-1.
The RTCC registers are contained in addresses 0x00-
0x1F. Table 5-1 shows the detailed RTCC register
map. There are 64 bytes of user-accessible SRAM,
located in the address range 0x20-0x5F. The SRAM is
a separate block from the RTCC registers. All RTCC
registers and SRAM locations are maintained while
operating from backup power.
FIGURE 5-1: MEMORY MAP
Time and Date
SRAM (64 Bytes)
Power-Fail/Power-Up Time-Stamps
Alarm 1
Alarm 0
Configuration and Trimming
0x00
0x06
0x07
0x09
0x0A
0x10
0x11
0x17
0x18
0x1F
0x20
0x5F
0x60
0xFF
Unimplemented; device does not ACK
I2C Address: 1101111x
RTCC Registers/SRAM
2011-2018 Microchip Technology Inc. DS20005010G-page 12
MCP7940N
TABLE 5-1: DETAILED RTCC REGISTER MAP
Addr. Register Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Section 5.3 “Timekeeping”
00h RTCSEC ST SECTEN2 SECTEN1 SECTEN0 SECONE3 SECONE2 SECONE1 SECONE0
01h RTCMIN MINTEN2 MINTEN1 MINTEN0 MINONE3 MINONE2 MINONE1 MINONE0
02h RTCHOUR 12/24 AM/PM
HRTEN1
HRTEN0 HRONE3 HRONE2 HRONE1 HRONE0
03h RTCWKDAY OSCRUN PWRFAIL VBATEN WKDAY2 WKDAY1 WKDAY0
04h RTCDATE DATETEN1 DATETEN0 DATEONE3 DATEONE2 DATEONE1 DATEONE0
05h RTCMTH LPYR MTHTEN0 MTHONE3 MTHONE2 MTHONE1 MTHONE0
06h RTCYEAR YRTEN3 YRTEN2 YRTEN1 YRTEN0 YRONE3 YRONE2 YRONE1 YRONE0
07h CONTROL OUT SQWEN ALM1EN ALM0EN EXTOSC CRSTRIM SQWFS1 SQWFS0
08h OSCTRIM SIGN TRIMVAL6 TRIMVAL5 TRIMVAL4 TRIMVAL3 TRIMVAL2 TRIMVAL1 TRIMVAL0
09h Reserved Reserved – Do not use
Section 5.4 “Alarms”
0Ah ALM0SEC SECTEN2 SECTEN1 SECTEN0 SECONE3 SECONE2 SECONE1 SECONE0
0Bh ALM0MIN MINTEN2 MINTEN1 MINTEN0 MINONE3 MINONE2 MINONE1 MINONE0
0Ch ALM0HOUR — 12/24(2)AM/PM
HRTEN1
HRTEN0 HRONE3 HRONE2 HRONE1 HRONE0
0Dh ALM0WKDAY ALMPOL ALM0MSK2 ALM0MSK1 ALM0MSK0 ALM0IF WKDAY2 WKDAY1 WKDAY0
0Eh ALM0DATE DATETEN1 DATETEN0 DATEONE3 DATEONE2 DATEONE1 DATEONE0
0Fh ALM0MTH MTHTEN0 MTHONE3 MTHONE2 MTHONE1 MTHONE0
10h Reserved Reserved – Do not use
Section 5.4 “Alarms”
11h ALM1SEC SECTEN2 SECTEN1 SECTEN0 SECONE3 SECONE2 SECONE1 SECONE0
12h ALM1MIN MINTEN2 MINTEN1 MINTEN0 MINONE3 MINONE2 MINONE1 MINONE0
13h ALM1HOUR — 12/24(2)AM/PM
HRTEN1
HRTEN0 HRONE3 HRONE2 HRONE1 HRONE0
14h ALM1WKDAY ALMPOL(3)ALM1MSK2 ALM1MSK1 ALM1MSK0 ALM1IF WKDAY2 WKDAY1 WKDAY0
15h ALM1DATE DATETEN1 DATETEN0 DATEONE3 DATEONE2 DATEONE1 DATEONE0
16h ALM1MTH MTHTEN0 MTHONE3 MTHONE2 MTHONE1 MTHONE0
17h Reserved Reserved – Do not use
Section 5.7.1 “Power-Fail Time-Stamp”
18h PWRDNMIN MINTEN2 MINTEN1 MINTEN0 MINONE3 MINONE2 MINONE1 MINONE0
19h PWRDNHOUR 12/24 AM/PM
HRTEN1
HRTEN0 HRONE3 HRONE2 HRONE1 HRONE0
1Ah PWRDNDATE DATETEN1 DATETEN0 DATEONE3 DATEONE2 DATEONE1 DATEONE0
1Bh PWRDNMTH WKDAY2 WKDAY1 WKDAY0 MTHTEN0 MTHONE3 MTHONE2 MTHONE1 MTHONE0
Section 5.7.1 “Power-Fail Time-Stamp”
1Ch PWRUPMIN MINTEN2 MINTEN1 MINTEN0 MINONE3 MINONE2 MINONE1 MINONE0
1Dh PWRUPHOUR 12/24 AM/PM
HRTEN1
HRTEN0 HRONE3 HRONE2 HRONE1 HRONE0
1Eh PWRUPDATE DATETEN1 DATETEN0 DATEONE3 DATEONE2 DATEONE1 DATEONE0
1Fh PWRUPMTH WKDAY2 WKDAY1 WKDAY0 MTHTEN0 MTHONE3 MTHONE2 MTHONE1 MTHONE0
Note 1: Grey areas are unimplemented.
2: The 12/24 bits in the ALMxHOUR registers are read-only and reflect the value of the 12/24 bit in the
RTCHOUR register.
3: The ALMPOL bit in the ALM1WKDAY register is read-only and reflects the value of the ALMPOL bit in the
ALM0WKDAY register.
2011-2018 Microchip Technology Inc. DS20005010G-page 13
MCP7940N
5.2 Oscillator Configuration
The MCP7940N can be operated in two different oscil-
lator configurations: using an external crystal or using
an external clock input.
5.2.1 EXTERNAL CRYSTAL
The crystal oscillator circuit on the MCP7940N is
designed to operate with a standard 32.768 kHz tuning
fork crystal and matching external load capacitors. By
using external load capacitors, the MCP7940N allows
for a wide selection of crystals. Suitable crystals have
a load capacitance (CL) of 6-9 pF. Crystals with a load
capacitance of 12.5 pF are not recommended.
Figure 5-2 shows the pin connections when using an
external crystal.
FIGURE 5-2: CRYSTAL OPERATION
5.2.1.1 Choosing Load Capacitors
CL is the effective load capacitance as seen by the
crystal, and includes the physical load capacitors, pin
capacitance, and stray board capacitance. Equation 5-1
can be used to calculate CL.
CX1 and CX2 are the external load capacitors. They
must be chosen to match the selected crystal’s speci-
fied load capacitance.
EQUATION 5-1: LOAD CAPACITANCE
CALCULATION
5.2.1.2 Layout Considerations
The oscillator circuit should be placed on the same
side of the board as the device. Place the oscillator
circuit close to the respective oscillator pins. The load
capacitors should be placed next to the oscillator
itself, on the same side of the board.
Use a grounded copper pour around the oscillator cir-
cuit to isolate it from surrounding circuits. The
grounded copper pour should be routed directly to VSS.
Do not run any signal traces or power traces inside the
ground pour. Also, if using a two-sided board, avoid any
traces on the other side of the board where the crystal
is placed.
Layout suggestions are shown in Figure 5-3. In-line
packages may be handled with a single-sided layout
that completely encompasses the oscillator pins. With
fine-pitch packages, it is not always possible to com-
pletely surround the pins and components. A suitable
solution is to tie the broken guard sections to a mirrored
ground layer. In all cases, the guard trace(s) must be
returned to ground.
For additional information and design guidance on
oscillator circuits, refer to these Microchip Application
Notes, available at the corporate website
(www.microchip.com):
AN1365, “Recommended Usage of Microchip
Serial RTCC Devices”
AN1519, “Recommended Crystals for Microchip
Stand-Alone Real-Time Clock Calendar Devices”
Note 1: The ST bit must be set to enable the
crystal oscillator circuit.
2: Always verify oscillator performance over
the voltage and temperature range that is
expected for the application.
Note: If the load capacitance is not correctly
matched to the chosen crystal’s specified
value, the crystal may give a frequency
outside of the crystal manufacturer’s
specifications.
CX1
CX2
Quartz
X1
ST
To Internal
Logic
Crystal
X2
MCP7940N
CLCX1CX2
CX1CX2
+
---------------------------- C STRAY+=
Where:
CLEffective load capacitance=
CX1Capacitor value on X1 COSC+=
CX2Capacitor value on X2 COSC+=
CSTRAY PCB stray capacitance=
2011-2018 Microchip Technology Inc. DS20005010G-page 14
MCP7940N
FIGURE 5-3: SUGGESTED PLACEMENT OF THE OSCILLATOR CIRCUIT
5.2.2 EXTERNAL CLOCK INPUT
A 32.768 kHz external clock source can be connected
to the X1 pin (Figure 5-4). When using this configura-
tion, the X2 pin should be left floating.
FIGURE 5-4: EXTERNAL CLOCK INPUT
OPERATION
5.2.3 OSCILLATOR FAILURE STATUS
The MCP7940N features an oscillator failure flag,
OSCRUN, that indicates whether or not the oscillator is
running. The OSCRUN bit is automatically set after 32
oscillator cycles are detected. If no oscillator cycles are
detected for more than TOSF, then the OSCRUN bit is
automatically cleared (Figure 5-5). This can occur if the
oscillator is stopped by clearing the ST bit or due to
oscillator failure.
FIGURE 5-5: OSCILLATOR FAILURE STATUS TIMING DIAGRAM
TABLE 5-2: SUMMARY OF REGISTERS ASSOCIATED WITH OSCILLATOR CONFIGURATION
GND
`
X1
X2
DEVICE PINS
CX1
CX2
GND
X1
X2
Bottom Layer
Copper Pour
Oscillator
Crystal
Top Layer Copper Pour
CX1
CX2
DEVICE PINS
(tied to ground)
(tied to ground)
Single-Sided and In-line Layouts: Fine-Pitch (Dual-Sided) Layouts:
Oscillator
Crystal
Copper Pour
(tied to ground)
Note: The EXTOSC bit must be set to enable an
external clock source.
X1
Clock from
Ext. Source
MCP7940N
Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Register
on Page
RTCSEC ST SECTEN2 SECTEN1 SECTEN0 SECONE3 SECONE2 SECONE1 SECONE0 16
RTCWKDAY OSCRUN PWRFAIL VBATEN WKDAY2 WKDAY1 WKDAY0 18
CONTROL OUT SQWEN ALM1EN ALM0EN EXTOSC CRSTRIM SQWFS1 SQWFS0 26
Legend: = unimplemented location, read as ‘0’. Shaded cells are not used by oscillator configuration.
X1
OSCRUN Bit
< TOSF TOSF
32 Clock Cycles
2011-2018 Microchip Technology Inc. DS20005010G-page 15
MCP7940N
5.3 Timekeeping
The MCP7940N maintains the current time and date
using an external 32.768 kHz crystal or clock source.
Separate registers are used for tracking seconds, min-
utes, hours, day of week, date, month, and year. The
MCP7940N automatically adjusts for months with less
than 31 days and compensates for leap years from
2001 to 2399. The year is stored as a two-digit value.
Both 12-hour and 24-hour time formats are supported
and are selected using the 12/24 bit.
The day of week value counts from 1 to 7, increments
at midnight, and the representation is user-defined (i.e.,
the MCP7940N does not require 1 to equal Sunday,
etc.).
All time and date values are stored in the registers as
binary-coded decimal (BCD) values. The MCP7940N
will continue to maintain the time and date while oper-
ating off the backup supply.
When reading from the timekeeping registers, the reg-
isters are buffered to prevent errors due to rollover of
counters. The following events cause the buffers to be
updated:
When a read is initiated from the RTCC registers
(addresses 0x00 to 0x1F)
During an RTCC register read operation, when
the register address rolls over from 0x1F to 0x00
The timekeeping registers should be read in a single
operation to utilize the on-board buffers and avoid
rollover issues.
5.3.1 DIGIT CARRY RULES
The following list explains which timer values cause a
digit carry when there is a rollover:
Time of day: from 11:59:59 PM to 12:00:00 AM
(12-hour mode) or 23:59:59 to 00:00:00 (24-hour
mode), with a carry to the Date and Weekday
fields
Date: carries to the Month field according to Table
5-3
Weekday: from 7 to 1 with no carry
Month: from 12/31 to 01/01 with a carry to the
Year field
Year: from 99 to 00 with no carry
TABLE 5-3: DAY TO MONTH ROLLOVER
SCHEDULE
Note 1: Loading invalid values into the time and
date registers will result in undefined
operation.
2: To avoid rollover issues when loading
new time and date values, the oscillator/
clock input should be disabled by clearing
the ST bit for External Crystal mode and
the EXTOSC bit for External Clock Input
mode. After waiting for the OSCRUN bit
to clear, the new values can be loaded
and the ST or EXTOSC bit can then be
re-enabled.
Month Name Maximum Date
01 January 31
02 February 28 or 29(1)
03 March 31
04 April 30
05 May 31
06 June 30
07 July 31
08 August 31
09 September 30
10 October 31
11 November 30
12 December 31
Note 1: 29 during leap years, otherwise 28.
2011-2018 Microchip Technology Inc. DS20005010G-page 16
MCP7940N
REGISTER 5-1: RTCSEC: TIMEKEEPING SECONDS VALUE REGISTER (ADDRESS 0x00)
R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0
ST SECTEN2 SECTEN1 SECTEN0 SECONE3 SECONE2 SECONE1 SECONE0
bit 7 bit 0
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is clear x = Bit is unknown
bit 7 ST: Start Oscillator bit
1 = Oscillator enabled
0 = Oscillator disabled
bit 6-4 SECTEN<2:0>: Binary-Coded Decimal Value of Second’s Tens Digit
Contains a value from 0 to 5
bit 3-0 SECONE<3:0>: Binary-Coded Decimal Value of Second’s Ones Digit
Contains a value from 0 to 9
2011-2018 Microchip Technology Inc. DS20005010G-page 17
MCP7940N
REGISTER 5-2: RTCMIN: TIMEKEEPING MINUTES VALUE REGISTER (ADDRESS 0x01)
U-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0
MINTEN2 MINTEN1 MINTEN0 MINONE3 MINONE2 MINONE1 MINONE0
bit 7 bit 0
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is clear x = Bit is unknown
bit 7 Unimplemented: Read as ‘0
bit 6-4 MINTEN<2:0>: Binary-Coded Decimal Value of Minute’s Tens Digit
Contains a value from 0 to 5
bit 3-0 MINONE<3:0>: Binary-Coded Decimal Value of Minute’s Ones Digit
Contains a value from 0 to 9
REGISTER 5-3: RTCHOUR: TIMEKEEPING HOURS VALUE REGISTER (ADDRESS 0x02)
U-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0
12/24 AM/PM
HRTEN1
HRTEN0 HRONE3 HRONE2 HRONE1 HRONE0
bit 7 bit 0
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is clear x = Bit is unknown
If 12/24 = 1 (12-hour format):
bit 7 Unimplemented: Read as ‘0
bit 6 12/24: 12 or 24 Hour Time Format bit
1 = 12-hour format
0 = 24-hour format
bit 5 AM/PM: AM/PM Indicator bit
1 = PM
0 = AM
bit 4 HRTEN0: Binary-Coded Decimal Value of Hour’s Tens Digit
Contains a value from 0 to 1
bit 3-0 HRONE<3:0>: Binary-Coded Decimal Value of Hour’s Ones Digit
Contains a value from 0 to 9
If 12/24 = 0 (24-hour format):
bit 7 Unimplemented: Read as ‘0
bit 6 12/24: 12 or 24 Hour Time Format bit
1 = 12-hour format
0 = 24-hour format
bit 5-4 HRTEN<1:0>: Binary-Coded Decimal Value of Hour’s Tens Digit
Contains a value from 0 to 2.
bit 3-0 HRONE<3:0>: Binary-Coded Decimal Value of Hour’s Ones Digit
Contains a value from 0 to 9
2011-2018 Microchip Technology Inc. DS20005010G-page 18
MCP7940N
REGISTER 5-4: RTCWKDAY: TIMEKEEPING WEEKDAY VALUE REGISTER (ADDRESS 0x03)
U-0 U-0 R-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-1
OSCRUN PWRFAIL VBATEN WKDAY2 WKDAY1 WKDAY0
bit 7 bit 0
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is clear x = Bit is unknown
bit 7-6 Unimplemented: Read as ‘0
bit 5 OSCRUN: Oscillator Status bit
1 = Oscillator is enabled and running
0 = Oscillator has stopped or has been disabled
bit 4 PWRFAIL: Power Failure Status bit(1,2)
1 = Primary power was lost and the power-fail time-stamp registers have been loaded (must be
cleared in software). Clearing this bit resets the power-fail time-stamp registers to ‘0’.
0 = Primary power has not been lost
bit 3 VBATEN: External Battery Backup Supply (VBAT) Enable bit
1 = VBAT input is enabled
0 = VBAT input is disabled
bit 2-0 WKDAY<2:0>: Binary-Coded Decimal Value of Day of Week
Contains a value from 1 to 7. The representation is user-defined.
Note 1: The PWRFAIL bit must be cleared to log new time-stamp data. This is to ensure previous time-stamp data
is not lost.
2: The PWRFAIL bit cannot be written to a ‘1’ in software. Writing to the RTCWKDAY register will always
clear the PWRFAIL bit.
REGISTER 5-5: RTCDATE: TIMEKEEPING DATE VALUE REGISTER (ADDRESS 0x04)
U-0 U-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-1
DATETEN1 DATETEN0 DATEONE3 DATEONE2 DATEONE1 DATEONE0
bit 7 bit 0
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is clear x = Bit is unknown
bit 7-6 Unimplemented: Read as ‘0
bit 5-4 DATETEN<1:0>: Binary-Coded Decimal Value of Date’s Tens Digit
Contains a value from 0 to 3
bit 3-0 DATEONE<3:0>: Binary-Coded Decimal Value of Date’s Ones Digit
Contains a value from 0 to 9
2011-2018 Microchip Technology Inc. DS20005010G-page 19
MCP7940N
TABLE 5-4: SUMMARY OF REGISTERS ASSOCIATED WITH TIMEKEEPING
REGISTER 5-6: RTCMTH: TIMEKEEPING MONTH VALUE REGISTER (ADDRESS 0x05)
U-0 U-0 R-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-1
LPYR MTHTEN0 MTHONE3 MTHONE2 MTHONE1 MTHONE0
bit 7 bit 0
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is clear x = Bit is unknown
bit 7-6 Unimplemented: Read as ‘0
bit 5 LPYR: Leap Year bit
1 = Year is a leap year
0 = Year is not a leap year
bit 4 MTHTEN0: Binary-Coded Decimal Value of Month’s Tens Digit
Contains a value of 0 or 1
bit 3-0 MTHONE<3:0>: Binary-Coded Decimal Value of Month’s Ones Digit
Contains a value from 0 to 9
REGISTER 5-7: RTCYEAR: TIMEKEEPING YEAR VALUE REGISTER (ADDRESS 0x06)
R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-1
YRTEN3 YRTEN2 YRTEN1 YRTEN0 YRONE3 YRONE2 YRONE1 YRONE0
bit 7 bit 0
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is clear x = Bit is unknown
bit 7-4 YRTEN<3:0>: Binary-Coded Decimal Value of Year’s Tens Digit
Contains a value from 0 to 9
bit 3-0 YRONE<3:0>: Binary-Coded Decimal Value of Year’s Ones Digit
Contains a value from 0 to 9
Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Register
on Page
RTCSEC ST SECTEN2 SECTEN1 SECTEN0 SECONE3 SECONE2 SECONE1 SECONE0 16
RTCMIN MINTEN2 MINTEN1 MINTEN0 MINONE3 MINONE2 MINONE1 MINONE0 17
RTCHOUR 12/24 AM/PM
HRTEN1
HRTEN0 HRONE3 HRONE2 HRONE1 HRONE0 17
RTCWKDAY OSCRUN PWRFAIL VBATEN WKDAY2 WKDAY1 WKDAY0 18
RTCDATE DATETEN1 DATETEN0 DATEONE3 DATEONE2 DATEONE1 DATEONE0 18
RTCMTH LPYR MTHTEN0 MTHONE3 MTHONE2 MTHONE1 MTHONE0 19
RTCYEAR YRTEN3 YRTEN2 YRTEN1 YRTEN0 YRONE3 YRONE2 YRONE1 YRONE0 19
Legend: = unimplemented location, read as ‘0’. Shaded cells are not used in timekeeping.
2011-2018 Microchip Technology Inc. DS20005010G-page 20
MCP7940N
5.4 Alarms
The MCP7940N features two independent alarms.
Each alarm can be used to either generate an interrupt
at a specific time in the future, or to generate a periodic
interrupt every minute, hour, day, day of week, or
month.
There is a separate interrupt flag, ALMxIF, for each
alarm. The interrupt flags are set by hardware when the
chosen alarm mask condition matches (Table 5-5).
The interrupt flags must be cleared in software.
If either alarm module is enabled by setting the corre-
sponding ALMxEN bit in the CONTROL register, and if
the square wave clock output is disabled (SQWEN =
0), then the MFP will operate in Alarm Interrupt Output
mode. Refer to Section 5.5 “Output Configurations”
for details. The alarm interrupt output is available while
operating from the backup power supply.
Both Alarm0 and Alarm1 offer identical operation. All
time and date values are stored in the registers as
binary-coded decimal (BCD) values.
TABLE 5-5: ALARM MASKS
FIGURE 5-6: ALARM BLOCK DIAGRAM
Note: Throughout this section, references to the
register and bit names for the alarm mod-
ules are referred to generically by the use
of ‘x’ in place of the specific module num-
ber. Thus, “ALMxSEC” might refer to the
seconds register for Alarm0 or Alarm1.
ALMxMSK<2:0> Alarm Asserts on Match of
000 Seconds
001 Minutes
010 Hours
011 Day of Week
100 Date
101 Reserved
110 Reserved
111 Seconds, Minutes, Hours, Day of
Week, Date, and Month
Note 1: The alarm interrupt flags must be cleared
by the user. If a flag is cleared while the
corresponding alarm condition still
matches, the flag will be set again, gener-
ating another interrupt.
2: Loading invalid values into the alarm reg-
isters will result in undefined operation.
MFP
RTCSEC
RTCMIN
RTCHOUR
RTCWKDAY
RTCDATE
RTCMTH
Timekeeping
Registers
ALM1SEC
ALM1MIN
ALM1HOUR
ALM1WKDAY
ALM1DATE
ALM1MTH
Alarm1
Registers
ALM0SEC
ALM0MIN
ALM0HOUR
ALM0WKDAY
ALM0DATE
ALM0MTH
Alarm0
Registers
Alarm0 Mask Alarm1 MaskComparator Comparator
MFP Output Logic
Set
ALM0IF
Set
ALM1IF
ALM0MSK<2:0> ALM1MSK<2:0>
2011-2018 Microchip Technology Inc. DS20005010G-page 21
MCP7940N
5.4.1 CONFIGURING THE ALARM
In order to configure the alarm modules, the following
steps need to be performed:
1. Load the timekeeping registers and enable the
oscillator
2. Configure the ALMxMSK<2:0> bits to select the
desired alarm mask
3. Set or clear the ALMPOL bit according to the
desired output polarity
4. Ensure the ALMxIF flag is cleared
5. Based on the selected alarm mask, load the
alarm match value into the appropriate regis-
ter(s)
6. Enable the alarm module by setting the
ALMxEN bit
REGISTER 5-8: ALMxSEC: ALARM0/1 SECONDS VALUE REGISTER (ADDRESSES 0x0A/0x11)
U-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0
SECTEN2 SECTEN1 SECTEN0 SECONE3 SECONE2 SECONE1 SECONE0
bit 7 bit 0
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is clear x = Bit is unknown
bit 7 Unimplemented: Read as ‘0
bit 6-4 SECTEN<2:0>: Binary-Coded Decimal Value of Second’s Tens Digit
Contains a value from 0 to 5
bit 3-0 SECONE<3:0>: Binary-Coded Decimal Value of Second’s Ones Digit
Contains a value from 0 to 9
REGISTER 5-9: ALMxMIN: ALARM0/1 MINUTES VALUE REGISTER (ADDRESSES 0x0B/0x12)
U-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0
MINTEN2 MINTEN1 MINTEN0 MINONE3 MINONE2 MINONE1 MINONE0
bit 7 bit 0
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is clear x = Bit is unknown
bit 7 Unimplemented: Read as ‘0
bit 6-4 MINTEN<2:0>: Binary-Coded Decimal Value of Minute’s Tens Digit
Contains a value from 0 to 5
bit 3-0 MINONE<3:0>: Binary-Coded Decimal Value of Minute’s Ones Digit
Contains a value from 0 to 9
2011-2018 Microchip Technology Inc. DS20005010G-page 22
MCP7940N
REGISTER 5-10: ALMxHOUR: ALARM0/1 HOURS VALUE REGISTER (ADDRESSES 0x0C/0x13)
U-0 R-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0
12/24 AM/PM
HRTEN1
HRTEN0 HRONE3 HRONE2 HRONE1 HRONE0
bit 7 bit 0
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is clear x = Bit is unknown
If 12/24 = 1 (12-hour format):
bit 7 Unimplemented: Read as ‘0
bit 6 12/24: 12 or 24 Hour Time Format bit(1)
1 = 12-hour format
0 = 24-hour format
bit 5 AM/PM: AM/PM Indicator bit
1 = PM
0 = AM
bit 4 HRTEN0: Binary-Coded Decimal Value of Hour’s Tens Digit
Contains a value from 0 to 1
bit 3-0 HRONE<3:0>: Binary-Coded Decimal Value of Hour’s Ones Digit
Contains a value from 0 to 9
If 12/24 = 0 (24-hour format):
bit 7 Unimplemented: Read as ‘0
bit 6 12/24: 12 or 24 Hour Time Format bit(1)
1 = 12-hour format
0 = 24-hour format
bit 5-4 HRTEN<1:0>: Binary-Coded Decimal Value of Hour’s Tens Digit
Contains a value from 0 to 2.
bit 3-0 HRONE<3:0>: Binary-Coded Decimal Value of Hour’s Ones Digit
Contains a value from 0 to 9
Note 1: This bit is read-only and reflects the value of the 12/24 bit in the RTCHOUR register.
2011-2018 Microchip Technology Inc. DS20005010G-page 23
MCP7940N
REGISTER 5-11: ALMxWKDAY: ALARM0/1 WEEKDAY VALUE REGISTER (ADDRESSES 0x0D/
0x14)
R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-1
ALMPOL ALMxMSK2 ALMxMSK1 ALMxMSK0 ALMxIF WKDAY2 WKDAY1 WKDAY0
bit 7 bit 0
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is clear x = Bit is unknown
bit 7 ALMPOL: Alarm Interrupt Output Polarity bit
1 = Asserted output state of MFP is a logic high level
0 = Asserted output state of MFP is a logic low level
bit 6-4 ALMxMSK<2:0>: Alarm Mask bits
000 = Seconds match
001 = Minutes match
010 = Hours match (logic takes into account 12-/24-hour operation)
011 = Day of week match
100 = Date match
101 = Reserved; do not use
110 = Reserved; do not use
111 = Seconds, Minutes, Hour, Day of Week, Date and Month
bit 3 ALMxIF: Alarm Interrupt Flag bit(1,2)
1 = Alarm match occurred (must be cleared in software)
0 = Alarm match did not occur
bit 2-0 WKDAY<2:0>: Binary-Coded Decimal Value of Day bits
Contains a value from 1 to 7. The representation is user-defined.
Note 1: If a match condition still exists when this bit is cleared, it will be set again automatically.
2: The ALMxIF bit cannot be written to a 1 in software. Writing to the ALMxWKDAY register will always clear
the ALMxIF bit.
REGISTER 5-12: ALMxDATE: ALARM0/1 DATE VALUE REGISTER (ADDRESSES 0x0E/0x15)
U-0 U-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-1
DATETEN1 DATETEN0 DATEONE3 DATEONE2 DATEONE1 DATEONE0
bit 7 bit 0
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is clear x = Bit is unknown
bit 7-6 Unimplemented: Read as ‘0
bit 5-4 DATETEN<1:0>: Binary-Coded Decimal Value of Date’s Tens Digit
Contains a value from 0 to 3
bit 3-0 DATEONE<3:0>: Binary-Coded Decimal Value of Date’s Ones Digit
Contains a value from 0 to 9
2011-2018 Microchip Technology Inc. DS20005010G-page 24
MCP7940N
TABLE 5-6: SUMMARY OF REGISTERS ASSOCIATED WITH ALARMS
REGISTER 5-13: ALMxMTH: ALARM0/1 MONTH VALUE REGISTER (ADDRESSES 0x0F/0x16)
U-0 U-0 U-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-1
MTHTEN0 MTHONE3 MTHONE2 MTHONE1 MTHONE0
bit 7 bit 0
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is clear x = Bit is unknown
bit 7-5 Unimplemented: Read as ‘0
bit 4 MTHTEN0: Binary-Coded Decimal Value of Month’s Tens Digit
Contains a value of 0 or 1
bit 3-0 MTHONE<3:0>: Binary-Coded Decimal Value of Month’s Ones Digit
Contains a value from 0 to 9
Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Register
on Page
ALM0SEC SECTEN2 SECTEN1 SECTEN0 SECONE3 SECONE2 SECONE1 SECONE0 21
ALM0MIN MINTEN2 MINTEN1 MINTEN0 MINONE3 MINONE2 MINONE1 MINONE0 21
ALM0HOUR 12/24 AM/PM
HRTEN1
HRTEN0 HRONE3 HRONE2 HRONE1 HRONE0 22
ALM0WKDAY ALMPOL ALM0MSK2 ALM0MSK1 ALM0MSK0 ALM0IF WKDAY2 WKDAY1 WKDAY0 23
ALM0DATE DATETEN1 DATETEN0 DATEONE3 DATEONE2 DATEONE1 DATEONE0 23
ALM0MTH MTHTEN0 MTHONE3 MTHONE2 MTHONE1 MTHONE0 24
ALM1SEC SECTEN2 SECTEN1 SECTEN0 SECONE3 SECONE2 SECONE1 SECONE0 21
ALM1MIN MINTEN2 MINTEN1 MINTEN0 MINONE3 MINONE2 MINONE1 MINONE0 21
ALM1HOUR 12/24 AM/PM
HRTEN1
HRTEN0 HRONE3 HRONE2 HRONE1 HRONE0 22
ALM1WKDAY ALMPOL ALM1MSK2 ALM1MSK1 ALM1MSK0 ALM1IF WKDAY2 WKDAY1 WKDAY0 23
ALM1DATE DATETEN1 DATETEN0 DATEONE3 DATEONE2 DATEONE1 DATEONE0 23
ALM1MTH MTHTEN0 MTHONE3 MTHONE2 MTHONE1 MTHONE0 24
CONTROL OUT SQWEN ALM1EN ALM0EN EXTOSC CRSTRIM SQWFS1 SQWFS0 26
Legend: = unimplemented location, read as ‘0’. Shaded cells are not used by alarms.
2011-2018 Microchip Technology Inc. DS20005010G-page 25
MCP7940N
5.5 Output Configurations
The MCP7940N features Square Wave Clock Output,
Alarm Interrupt Output, and General Purpose Output
modes. All of the output functions are multiplexed onto
MFP according to Table 5-7.
Only the alarm interrupt outputs are available while
operating from the backup power supply. If none of the
output functions are being used, the MFP can safely be
left floating.
TABLE 5-7: MFP OUTPUT MODES
FIGURE 5-7: MFP OUTPUT BLOCK DIAGRAM
Note: The MFP is an open-drain output and
requires a pull-up resistor to VCC (typically
10 k).
SQWEN ALM0EN ALM1EN Mode
000
General Purpose
Output
010
Alarm Interrupt
Output
001
011
1xx
Square Wave Clock
Output
X2
X1
ST
Oscillator
EXTOSC
Postscaler
MUX
32.768 kHz
8.192 kHz
4.096 kHz
1 Hz
SQWFS<1:0>
11
10
01
00
Digital
Trim
1
0
64 Hz
CRSTRIM
MFP
0
1
SQWEN
0
1
0
1
ALM1IF
ALM0IF
ALMPOL
MUX
ALM1EN,ALM0EN
11
10
01
00
OUT
MCP7940N
‘ c ‘ c I
2011-2018 Microchip Technology Inc. DS20005010G-page 26
MCP7940N
REGISTER 5-14: CONTROL: RTCC CONTROL REGISTER (ADDRESS 0x07)
R/W-1 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0
OUT SQWEN ALM1EN ALM0EN EXTOSC CRSTRIM SQWFS1 SQWFS0
bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is clear x = Bit is unknown
bit 7 OUT: Logic Level for General Purpose Output bit
Square Wave Clock Output Mode (SQWEN = 1):
Unused.
Alarm Interrupt Output mode (ALM0EN = 1 or ALM1EN = 1):
Unused.
General Purpose Output mode (SQWEN = 0, ALM0EN = 0, and ALM1EN = 0):
1 = MFP signal level is logic high
0 = MFP signal level is logic low
bit 6 SQWEN: Square Wave Output Enable bit
1 = Enable Square Wave Clock Output mode
0 = Disable Square Wave Clock Output mode
bit 5 ALM1EN: Alarm 1 Module Enable bit
1 = Alarm 1 enabled
0 = Alarm 1 disabled
bit 4 ALM0EN: Alarm 0 Module Enable bit
1 = Alarm 0 enabled
0 = Alarm 0 disabled
bit 3 EXTOSC: External Oscillator Input bit
1 = Enable X1 pin to be driven by external 32.768 kHz source
0 = Disable external 32.768 kHz input
bit 2 CRSTRIM: Coarse Trim Mode Enable bit
Coarse Trim mode results in the MCP7940N applying digital trimming every 64 Hz clock cycle.
1 = Enable Coarse Trim mode. If SQWEN = 1, MFP will output trimmed 64 Hz(1) nominal clock signal.
0 = Disable Coarse Trim mode
See Section 5.6 “Digital Trimming” for details
bit 1-0 SQWFS<1:0>: Square Wave Clock Output Frequency Select bits
If SQWEN = 1 and CRSTRIM = 0:
Selects frequency of clock output on MFP
00 = 1 Hz(1)
01 = 4.096 kHz(1)
10 = 8.192 kHz(1)
11 = 32.768 kHz
If SQWEN = 0 or CRSTRIM = 1:
Unused.
Note 1: The 8.192 kHz, 4.096 kHz, 64 Hz, and 1 Hz square wave clock output frequencies are affected by digital
trimming.
2011-2018 Microchip Technology Inc. DS20005010G-page 27
MCP7940N
5.5.1 SQUARE WAVE OUTPUT MODE
The MCP7940N can be configured to generate a
square wave clock signal on MFP. The input clock
frequency, FOSC, is divided according to the
SQWFS<1:0> bits as shown in Table 5-8.
The square wave output is not available when operat-
ing from the backup power supply.
TABLE 5-8: CLOCK OUTPUT RATES
5.5.2 ALARM INTERRUPT OUTPUT
MODE
The MFP will provide an interrupt output when enabled
alarms match and the square wave clock output is dis-
abled. This prevents the user from having to poll the
alarm interrupt flag to check for a match.
The alarm interrupt output is available when operating
from the backup power supply.
The ALMxIF flags control when the MFP is asserted, as
described in the following sections.
5.5.2.1 Single Alarm Operation
When only one alarm module is enabled, the MFP output
is based on the corresponding ALMxIF flag and the
ALMPOL flag. If ALMPOL = 1, the MFP output reflects
the value of the ALMxIF flag. If ALMPOL = 0, the MFP
output reflects the inverse of the ALMxIF flag (Table 5-
9).
TABLE 5-9: SINGLE ALARM OUTPUT
TRUTH TABLE
5.5.2.2 Dual Alarm Operation
When both alarm modules are enabled, the MFP out-
put is determined by a combination of the ALM0IF,
ALM1IF, and ALMPOL flags.
If ALMPOL = 1, the ALM0IF and ALM1IF flags are
OR’d together and the result is output on MFP. If
ALMPOL = 0, the ALM0IF and ALM1IF flags are AND’d
together, and the result is inverted and output on MFP
(Table 5-10). This provides the user with flexible
options for combining alarms.
TABLE 5-10: DUAL ALARM OUTPUT
TRUTH TABLE
5.5.3 GENERAL PURPOSE OUTPUT
MODE
If the square wave clock output and both alarm mod-
ules are disabled, the MFP acts as a general purpose
output. The output logic level is controlled by the OUT
bit.
The general purpose output is not available when
operating from the backup power supply.
Note: All of the clock output rates are affected by
digital trimming except for the 1:1
postscaler value (SQWFS<1:0> = 11).
SQWFS<1:0> Postscaler Nominal
Frequency
00 1:32,768 1 Hz
01 1:8 4.096 kHz
10 1:4 8.192 kHz
11 1:1 32.768 kHz
Note 1: Nominal frequency assumes FOSC is
32.768 kHz.
ALMPOL ALMxIF(1)MFP
001
010
100
111
Note 1: ALMxIF refers to the interrupt flag corre-
sponding to the alarm module that is
enabled.
Note: If ALMPOL = 0 and both alarms are
enabled, the MFP will only assert when
both ALM0IF and ALM1IF are set.
ALMPOL ALM0IF ALM1IF MFP
0001
0011
0101
0110
1000
1011
1101
1111
2011-2018 Microchip Technology Inc. DS20005010G-page 28
MCP7940N
TABLE 5-11: SUMMARY OF REGISTERS ASSOCIATED WITH OUTPUT CONFIGURATION
Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Register
on Page
ALM0WKDAY ALMPOL ALM0MSK2 ALM0MSK1 ALM0MSK0 ALM0IF WKDAY2 WKDAY1 WKDAY0 23
ALM1WKDAY ALMPOL ALM1MSK2 ALM1MSK1 ALM1MSK0 ALM1IF WKDAY2 WKDAY1 WKDAY0 23
CONTROL OUT SQWEN ALM1EN ALM0EN EXTOSC CRSTRIM SQWFS1 SQWFS0 26
Legend: = unimplemented location, read as ‘0’. Shaded cells are not used in output configuration.
he
2011-2018 Microchip Technology Inc. DS20005010G-page 29
MCP7940N
5.6 Digital Trimming
The MCP7940N features digital trimming to correct for
inaccuracies of the external crystal or clock source, up
to roughly ±129 PPM when CRSTRIM = 0. In addition
to compensating for intrinsic inaccuracies in the clock,
this feature can also be used to correct for error due to
temperature variation. This can enable the user to
achieve high levels of accuracy across a wide tempera-
ture operating range.
Digital trimming consists of the MCP7940N periodically
adding or subtracting clock cycles, resulting in small
adjustments in the internal timing. The adjustment
occurs once per minute when CRSTRIM = 0. The SIGN
bit specifies whether to add cycles or to subtract them.
The TRIMVAL<6:0> bits are used to specify by how
many clock cycles to adjust. Each step in the
TRIMVAL<6:0> value equates to adding or subtracting
two clock pulses to or from the 32.768 kHz clock signal.
This results in a correction of roughly 1.017 PPM per
step when CRSTRIM = 0. Setting TRIMVAL<6:0> to
0x00 disables digital trimming.
Digital trimming also occurs while operating off the
backup supply.
REGISTER 5-15: OSCTRIM: OSCILLATOR DIGITAL TRIM REGISTER (ADDRESS 0x08)
R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0
SIGN TRIMVAL6 TRIMVAL5 TRIMVAL4 TRIMVAL3 TRIMVAL2 TRIMVAL1 TRIMVAL0
bit 7 bit 0
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is clear x = Bit is unknown
bit 7 SIGN: Trim Sign bit
1 = Add clocks to correct for slow time
0 = Subtract clocks to correct for fast time
bit 6-0 TRIMVAL<6:0>: Oscillator Trim Value bits
When CRSTRIM = 0:
1111111 = Add or subtract 254 clock cycles every minute
1111110 = Add or subtract 252 clock cycles every minute
0000010 = Add or subtract 4 clock cycles every minute
0000001 = Add or subtract 2 clock cycles every minute
0000000 = Disable digital trimming
When CRSTRIM = 1:
1111111 = Add or subtract 254 clock cycles 128 times per second
1111110 = Add or subtract 252 clock cycles 128 times per second
0000010 = Add or subtract 4 clock cycles 128 times per second
0000001 = Add or subtract 2 clock cycles 128 times per second
0000000 = Disable digital trimming
2011-2018 Microchip Technology Inc. DS20005010G-page 30
MCP7940N
5.6.1 CALIBRATION
In order to perform calibration, the number of error
clock pulses per minute must be found and the corre-
sponding trim value must be loaded into
TRIMVAL<6:0>.
There are two methods for determining the trim value.
The first method involves measuring an output fre-
quency directly and calculating the deviation from ideal.
The second method involves observing the number of
seconds gained or lost over a period of time.
Once the OSCTRIM register has been loaded, digital
trimming will automatically occur every minute.
5.6.1.1 Calibration by Measuring Frequency
To calibrate the MCP7940N by measuring the output
frequency, perform the following steps:
1. Enable the crystal oscillator or external clock
input by setting the ST bit or EXTOSC bit,
respectively.
2. Ensure TRIMVAL<6:0> is reset to 0x00.
3. Select an output frequency by setting
SQWFS<1:0>.
4. Set SQWEN to enable the square wave output.
5. Measure the resulting output frequency using a
calibrated measurement tool, such as a
frequency counter.
6. Calculate the number of error clocks per minute
(see Equation 5-2).
EQUATION 5-2: CALCULATING TRIM
VALUE FROM MEASURED
FREQUENCY
If the number of error clocks per minute is
negative, then the oscillator is faster than
ideal and the SIGN bit must be cleared.
If the number of error clocks per minute is
positive, then the oscillator is slower than
ideal and the SIGN bit must be set.
7. Load the correct value into TRIMVAL<6:0>.
5.6.1.2 Calibration by Observing Time
Deviation
To calibrate the MCP7940N by observing the deviation
over time, perform the following steps:
1. Ensure TRIMVAL<6:0> is reset to 0x00.
2. Load the timekeeping registers to synchronize
the MCP7940N with a known-accurate refer-
ence time.
3. Enable the crystal oscillator or external clock
input by setting the ST bit or EXTOSC bit,
respectively.
4. Observe how many seconds are gained or lost
over a period of time (larger time periods offer
more accuracy).
5. Calculate the PPM deviation (see Equation 5-3).
EQUATION 5-3: CALCULATING ERROR
PPM
If the MCP7940N has gained time relative to
the reference clock, then the oscillator is
faster than ideal and the SIGN bit must be
cleared.
If the MCP7940N has lost time relative to the
reference clock, then the oscillator is slower
than ideal and the SIGN bit must be set.
6. Calculate the trim value (see Equation 5-4).
EQUATION 5-4: CALCULATING TRIM
VALUE FROM ERROR
PPM
7. Load the correct value into TRIMVAL<6:0>.
Note: Using a lower output frequency and/or
averaging the measured frequency over a
number of clock pulses will reduce the
effects of jitter and improve accuracy.
TRIMVAL<6:0>
FIDEAL FMEAS
32768
FIDEAL
-------------------60
2
----------------------------------------------------------------------------------
=
Where:
FIDEAL Ideal frequency based on SQWFS<1:0>=
FMEAS Measured frequency=
Note 1: Choosing a longer time period for observ-
ing deviation will improve accuracy.
2: Large temperature variations during the
observation period can skew results.
PPM SecDeviation
ExpectedSec
----------------------------------- 1000000=
Where:
ExpectedSec Number of seconds in chosen period=
SecDeviation Number of seconds gained or lost=
TRIMVAL<6:0> PPM 32768 60
1000000 2
--------------------------------------------
=
2011-2018 Microchip Technology Inc. DS20005010G-page 31
MCP7940N
5.6.2 COARSE TRIM MODE
When CRSTRIM = 1, Coarse Trim mode is enabled.
While in this mode, the MCP7940N will apply trimming
at a rate of 128 Hz. If SQWEN is set, the MFP will out-
put a trimmed 64 Hz nominal clock signal.
Because trimming is applied at a rate of 128 Hz rather
than once every minute, each step of the
TRIMVAL<6:0> value has a significantly larger effect
on the resulting time deviation and output clock
frequency.
By monitoring the MFP output frequency while in this
mode, the user can easily observe the TRIMVAL<6:0>
value affecting the clock timing.
TABLE 5-12: SUMMARY OF REGISTERS ASSOCIATED WITH DIGITAL TRIMMING
Note 1: The 64 Hz Coarse Trim mode square
wave output is not available while operat-
ing from the backup power supply.
2: With Coarse Trim mode enabled, the
TRIMVAL<6:0> value has a drastic effect
on timing. Leaving the mode enabled
during normal operation will likely result
in inaccurate time.
Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Register
on Page
CONTROL OUT SQWEN ALM1EN ALM0EN EXTOSC CRSTRIM SQWFS1 SQWFS0 26
OSCTRIM SIGN TRIMVAL6 TRIMVAL5 TRIMVAL4 TRIMVAL3 TRIMVAL2 TRIMVAL1 TRIMVAL0 29
Legend: = unimplemented location, read as ‘0’. Shaded cells are not used by digital trimming.
2011-2018 Microchip Technology Inc. DS20005010G-page 32
MCP7940N
5.7 Battery Backup
The MCP7940N features a backup power supply input
(VBAT) that can be used to provide power to the time-
keeping circuitry, RTCC registers, and SRAM while pri-
mary power is unavailable. The MCP7940N will
automatically switch to backup power when VCC falls
below VTRIP, and back to VCC when it is above VTRIP.
The VBATEN bit must be set to enable the VBAT input.
The following functionality is maintained while operat-
ing on backup power:
• Timekeeping
• Alarms
Alarm Output
Digital Trimming
RTCC Register and SRAM Contents
The following features are not available while operating
on backup power:
•I
2C Communication
Square Wave Clock Output
General Purpose Output
5.7.1 POWER-FAIL TIME-STAMP
The MCP7940N includes a power-fail time-stamp mod-
ule that stores the minutes, hours, date, and month
when primary power is lost and when it is restored
(Figure 5-8). The PWRFAIL bit is also set to indicate
that a power failure occurred.
To utilize the power-fail time-stamp feature, a backup
power supply must be available with the VBAT input
enabled, and the oscillator should also be running to
ensure accurate functionality.
FIGURE 5-8: POWER-FAIL TIME-STAMP TIMING
Note: Throughout this section, references to the
register and bit names for the Power-Fail
Time-Stamp module are referred to gener-
ically by the use of ‘x’ in place of the spe-
cific module name. Thus, “PWRxxMIN”
might refer to the minutes register for
Power-Down or Power-Up.
Note 1: The PWRFAIL bit must be cleared to log
new time-stamp data. This is to ensure
previous time-stamp data is not lost.
2: Clearing the PWRFAIL bit will clear all
time-stamp registers.
Power-Down Power-Up
Time-Stamp Time-Stamp
VCC
VTRIP
2011-2018 Microchip Technology Inc. DS20005010G-page 33
MCP7940N
REGISTER 5-16: PWRxxMIN: POWER-DOWN/POWER-UP TIME-STAMP MINUTES VALUE
REGISTER (ADDRESSES 0x18/0x1C)
U-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0
MINTEN2 MINTEN1 MINTEN0 MINONE3 MINONE2 MINONE1 MINONE0
bit 7 bit 0
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is clear x = Bit is unknown
bit 7 Unimplemented: Read as ‘0
bit 6-4 MINTEN<2:0>: Binary-Coded Decimal Value of Minute’s Tens Digit
Contains a value from 0 to 5
bit 3-0 MINONE<3:0>: Binary-Coded Decimal Value of Minute’s Ones Digit
Contains a value from 0 to 9
REGISTER 5-17: PWRxxHOUR: POWER-DOWN/POWER-UP TIME-STAMP HOURS VALUE
REGISTER (ADDRESSES 0x19/0x1D)
U-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0
12/24 AM/PM
HRTEN1
HRTEN0 HRONE3 HRONE2 HRONE1 HRONE0
bit 7 bit 0
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is clear x = Bit is unknown
If 12/24 = 1 (12-hour format):
bit 7 Unimplemented: Read as ‘0
bit 6 12/24: 12 or 24 Hour Time Format bit
1 = 12-hour format
0 = 24-hour format
bit 5 AM/PM: AM/PM Indicator bit
1 = PM
0 = AM
bit 4 HRTEN0: Binary-Coded Decimal Value of Hour’s Tens Digit
Contains a value from 0 to 1
bit 3-0 HRONE<3:0>: Binary-Coded Decimal Value of Hour’s Ones Digit
Contains a value from 0 to 9
If 12/24 = 0 (24-hour format):
bit 7 Unimplemented: Read as ‘0
bit 6 12/24: 12 or 24 Hour Time Format bit
1 = 12-hour format
0 = 24-hour format
bit 5-4 HRTEN<1:0>: Binary-Coded Decimal Value of Hour’s Tens Digit
Contains a value from 0 to 2.
bit 3-0 HRONE<3:0>: Binary-Coded Decimal Value of Hour’s Ones Digit
Contains a value from 0 to 9
2011-2018 Microchip Technology Inc. DS20005010G-page 34
MCP7940N
TABLE 5-13: SUMMARY OF REGISTERS ASSOCIATED WITH BATTERY BACKUP
REGISTER 5-18: PWRxxDATE: POWER-DOWN/POWER-UP TIME-STAMP DATE VALUE
REGISTER (ADDRESSES 0x1A/0x1E)
U-0 U-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0
DATETEN1 DATETEN0 DATEONE3 DATEONE2 DATEONE1 DATEONE0
bit 7 bit 0
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is clear x = Bit is unknown
bit 7-6 Unimplemented: Read as ‘0
bit 5-4 DATETEN<1:0>: Binary-Coded Decimal Value of Date’s Tens Digit
Contains a value from 0 to 3
bit 3-0 DATEONE<3:0>: Binary-Coded Decimal Value of Date’s Ones Digit
Contains a value from 0 to 9
REGISTER 5-19: PWRxxMTH: POWER-DOWN/POWER-UP TIME-STAMP MONTH VALUE
REGISTER (ADDRESSES 0x1B/0x1F)
R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0
WKDAY2 WKDAY1 WKDAY0 MTHTEN0 MTHONE3 MTHONE2 MTHONE1 MTHONE0
bit 7 bit 0
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is clear x = Bit is unknown
bit 7-5 WKDAY<2:0>: Binary-Coded Decimal Value of Day bits
Contains a value from 1 to 7. The representation is user-defined.
bit 4 MTHTEN0: Binary-Coded Decimal Value of Month’s Ones Digit
Contains a value of 0 or 1
bit 3-0 MTHONE<3:0>: Binary-Coded Decimal Value of Month’s Ones Digit
Contains a value from 0 to 9
Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Register
on Page
RTCWKDAY OSCRUN PWRFAIL VBATEN WKDAY2 WKDAY1 WKDAY0 18
PWRDNMIN MINTEN2 MINTEN1 MINTEN0 MINONE3 MINONE2 MINONE1 MINONE0 33
PWRDNHOUR 12/24 AM/PM
HRTEN1
HRTEN0 HRONE3 HRONE2 HRONE1 HRONE0 33
PWRDNDATE DATETEN1 DATETEN0 DATEONE3 DATEONE2 DATEONE1 DATEONE0 34
PWRDNMTH WKDAY2 WKDAY1 WKDAY0 MTHTEN0 MTHONE3 MTHONE2 MTHONE1 MTHONE0 34
PWRUPMIN MINTEN2 MINTEN1 MINTEN0 MINONE3 MINONE2 MINONE1 MINONE0 33
PWRUPHOUR 12/24 AM/PM
HRTEN1
HRTEN0 HRONE3 HRONE2 HRONE1 HRONE0 33
PWRUPDATE DATETEN1 DATETEN0 DATEONE3 DATEONE2 DATEONE1 DATEONE0 34
PWRUPMTH WKDAY2 WKDAY1 WKDAY0 MTHTEN0 MTHONE3 MTHONE2 MTHONE1 MTHONE0 34
Legend: = unimplemented location, read as ‘0’. Shaded cells are not used with battery backup.
U1U1H U1U11111111111 1111111
2011-2018 Microchip Technology Inc. DS20005010G-page 35
MCP7940N
6.0 ON-BOARD MEMORY
The MCP7940N has 64 bytes of SRAM for general pur-
pose usage. It is retained when the primary power
supply is removed if a backup supply is present and
enabled.
Although the SRAM is a separate block from the RTCC
registers, they are accessed using the same control
byte, ‘1101111X’.
6.1 SRAM/RTCC Registers
The RTCC registers are located at addresses 0x00 to
0x1F, and the SRAM is located at addresses 0x20 to
0x5F. The SRAM can be accessed while the RTCC reg-
isters are being internally updated. The SRAM is not
initialized by a Power-On Reset (POR).
Neither the RTCC registers nor the SRAM can be
accessed when the device is operating off the backup
power supply.
6.1.1 SRAM/RTCC REGISTER BYTE
WRITE
Following the Start condition from the master, the con-
trol code and the R/W bit (which is a logic low) are
clocked onto the bus by the master transmitter. This
indicates to the addressed slave receiver that the
address byte will follow after it has generated an
Acknowledge bit during the ninth clock cycle. There-
fore, the next byte transmitted by the master is the
address and will be written into the Address Pointer of
the MCP7940N. After receiving another Acknowledge
bit from the MCP7940N, the master device transmits
the data byte to be written into the addressed memory
location. The MCP7940N stores the data byte into
memory and acknowledges again, and the master gen-
erates a Stop condition (Figure 6-1).
If an attempt is made to write to an address past 0x5F,
the MCP7940N will not acknowledge the address or
data bytes, and no data will be written. After a byte
Write command, the internal Address Pointer will point
to the address location following the one that was just
written.
6.1.2 SRAM/RTCC REGISTER
SEQUENTIAL WRITE
The write control byte, address, and the first data byte
are transmitted to the MCP7940N in the same way as
in a byte write. But instead of generating a Stop condi-
tion, the master transmits additional data bytes. Upon
receipt of each byte, the MCP7940N responds with an
Acknowledge, during which the data is latched into
memory and the Address Pointer is internally incre-
mented by one. As with the byte write operation, the
master ends the command by generating a Stop condi-
tion (Figure 6-2).
There is no limit to the number of bytes that can be writ-
ten in a single command. However, because the RTCC
registers and SRAM are separate blocks, writing past
the end of each block will cause the Address Pointer to
roll over to the beginning of the same block. Specifi-
cally, the Address Pointer will roll over from 0x1F to
0x00, and from 0x5F to 0x20.
FIGURE 6-1: SRAM/RTCC BYTE WRITE
FIGURE 6-2: SRAM/RTCC SEQUENTIAL WRITE
BUS ACTIVITY
MASTER
SDA LINE
BUS ACTIVITY
S
T
A
R
T
CONTROL
BYTE
ADDRESS
BYTE DATA
S
T
O
P
A
C
K
A
C
K
A
C
K
S1101 0
111 P
0
BUS ACTIVITY
MASTER
SDA LINE
BUS ACTIVITY
S
T
A
R
T
CONTROL
BYTE
ADDRESS
BYTE DATA BYTE 0
S
T
O
P
A
C
K
A
C
K
A
C
K
DATA BYTE N
A
C
K
S1101 0
111 P
0
”HUM U‘U“‘|1111111 1UHH 371111111
2011-2018 Microchip Technology Inc. DS20005010G-page 36
MCP7940N
6.1.3 SRAM/RTCC REGISTER CURRENT
ADDRESS READ
The MCP7940N contains an address counter that
maintains the address of the last byte accessed, inter-
nally incremented by one. Therefore, if the previous
read access was to address n (n is any legal address),
the next current address read operation would access
data from address n + 1.
Upon receipt of the control byte with R/W bit set to ‘1’,
the MCP7940N issues an Acknowledge and transmits
the 8-bit data word. The master will not acknowledge
the transfer but does generate a Stop condition and the
MCP7940N discontinues transmission (Figure 6-3).
FIGURE 6-3: SRAM/RTCC CURRENT
ADDRESS READ
6.1.4 SRAM/RTCC REGISTER RANDOM
READ
Random read operations allow the master to access
any memory location in a random manner. To perform
this type of read operation, first the address must be
set. This is done by sending the address to the
MCP7940N as part of a write operation (R/W bit set to
0’). After the address is sent, the master generates a
Start condition following the Acknowledge. This termi-
nates the write operation, but not before the internal
Address Pointer is set. Then, the master issues the
control byte again but with the R/W bit set to a ‘1’. The
MCP7940N will then issue an Acknowledge and trans-
mit the 8-bit data word. The master will not acknowl-
edge the transfer but it does generate a Stop condition
which causes the MCP7940N to discontinue transmis-
sion (Figure 6-4). After a random Read command, the
internal address counter will point to the address loca-
tion following the one that was just read.
6.1.5 SRAM/RTCC REGISTER
SEQUENTIAL READ
Sequential reads are initiated in the same way as a
random read except that after the MCP7940N trans-
mits the first data byte, the master issues an Acknowl-
edge as opposed to the Stop condition used in a
random read. This Acknowledge directs the
MCP7940N to transmit the next sequentially
addressed 8-bit word (Figure 6-5). Following the final
byte transmitted to the master, the master will NOT
generate an Acknowledge but will generate a Stop con-
dition. To provide sequential reads, the MCP7940N
contains an internal Address Pointer which is incre-
mented by one at the completion of each operation.
This Address Pointer allows the entire memory block to
be serially read during one operation.
Because the RTCC registers and SRAM are separate
blocks, reading past the end of each block will cause
the Address Pointer to roll over to the beginning of the
same block. Specifically, the Address Pointer will roll
over from 0x1F to 0x00, and from 0x5F to 0x20.
FIGURE 6-4: SRAM/RTCC RANDOM READ
FIGURE 6-5: SRAM/RTCC SEQUENTIAL READ
BUS ACTIVITY
MASTER
SDA LINE
BUS ACTIVITY
P
S
S
T
O
P
CONTROL
BYTE
S
T
A
R
T
DATA
A
C
K
N
O
A
C
K
1011 1
BYTE
111
BUS ACTIVITY
MASTER
SDA LINE
BUS ACTIVITY
A
C
K
N
O
A
C
K
A
C
K
A
C
K
S
T
O
P
S
T
A
R
T
CONTROL
BYTE
ADDRESS
BYTE
CONTROL
BYTE
DATA
BYTE
S
T
A
R
T
S1101 0111 S1101 1 P111
BUS ACTIVITY
MASTER
SDA LINE
BUS ACTIVITY
CONTROL
BYTE DATA n DATA n + 1 DATA n + 2 DATA n + X
N
O
A
C
K
A
C
K
A
C
K
A
C
K
A
C
K
S
T
O
P
P
H HHH U UUU HHHH Q9 UUUH HHHH UUUU HHHH 940M UUUU HHHH CD HHUU HHHH UUUU F‘WH‘Wf‘Wfl CP794 as LALLALUJLJ
2011-2018 Microchip Technology Inc. DS20005010G-page 37
MCP7940N
7.0 PACKAGING INFORMATION
7.1 Package Marking Information
8-Lead SOIC (3.90 mm) Example:
XXXXXXXT
XXXXYYWW
NNN
8-Lead TSSOP Example:
7940NI
SN 1406
13F
8-Lead MSOP Example:
XXXX
TYWW
NNN
XXXXXT
YWWNNN
940N
I406
13F
7940NI
40613F
3
e
8-Lead 2x3 TDFN
XXX
YWW
NN
AAV
303
13
Example:
Part Number
1st Line Marking Codes
SOIC TSSOP MSOP TDFN PDIP
MCP7940N 7940NT 940N 7940NT AAV MCP7940N
T = Temperature grade
Legend: XX...X Customer-specific information
Y Year code (last digit of calendar year)
YY Year code (last 2 digits of calendar year)
WW Week code (week of January 1 is week ‘01’)
NNN Alphanumeric traceability code
JEDEC® designator for Matte Tin (Sn)
*This package is RoHs compliant. The JEDEC designator ( )
can be found on the outer packaging for this package.
Note: In the event the full Microchip part number cannot be marked on one line, it will
be carried over to the next line, thus limiting the number of available
characters for customer-specific information.
3
e
3
e
XXXXXXXX
T/XXXNNN
YYWW
8-Lead PDIP (300 mil) Example:
MCP7940N
I/P 13F
1406
3
e
8-Lead Plastic Small Outline (SN) - Narrow, 3.90 mm Body [SOIC] NOTE 1 E _ ‘+ 2x N/2 TlPS NX b t a El TOP VIEW A ‘— “- E-I — - -+— SEATING PLANE M 7 SIDE VIEW A ‘— * n L‘l VIEW A-A Mlcrochlp Technology Drawmg No (204—0579 Sheel 1 ol 2
2011-2018 Microchip Technology Inc. DS20005010G-page 38
MCP7940N
Note: For the most current package drawings, please see the Microchip Packaging Specification located at
http://www.microchip.com/packaging
B-Lead Plastic Small Outline (SN) - Narrow, 3.90 mm Body [SOIC] Units MILLlMETERS Dimension Lirriiis MIN l NOM l MAX Numoeroi Pins N 5 Pllch e 1.27 BSC Overall Heigm A . . 1.75 Molded Package Thlckness A2 1.25 . . Slandofl § A1 0.10 . 0.25 Overall Width E 6.00 BSC Molded Package Wldm E1 3.90 BSC Overall Length D 4.90 BSC Chamier (Optional) h 0.25 . 0.50 Foot Length L 0.40 . 1.27 Footprint L1 1.04 REF Foot Angle w 0“ . a“ Lead Thickness c 0.17 . 0.25 Lead width b 0.31 . 0.51 Mold Drafl Angle Top or 5“ - 15° Mold Drafl Angle aotiom fl 5° . 15° Notes: 1 Pin 1 Vlsual lndex feature may vary, but must oe located within the hatched area 2 §signiiicant Characteristic 3 Dlmensions D and E1 do not include mold flash or prulmsmns Mold flash or protrusions shall not exceed 0.15mrn per side 4 Dlmensicning arid ioleranoing per ASME 714 5M ESC' Basic Dimenslon Theorellcally Exact Value shown wllhuul tolerances REF' Reierence Dimension, usually Without tolerance. for iniormation purposes only Microchip Technology Drawing No c047057c Sheet 2 at 2
2011-2018 Microchip Technology Inc. DS20005010G-page 39
MCP7940N
Note: For the most current package drawings, please see the Microchip Packaging Specification located at
http://www.microchip.com/packaging
Notes: / S‘LK SCREEN LJULJ A x1 RECOMMENDED LAND PATI'ERN Umts MILUMETERS Dwmension mewts MIN \ NOM \ MAX Contact Pimh E 1.27 580 Contad Pad Spacmg c 5.40 Comad Pad deth (x3) x1 0.50 Contad Pad Lenglh (x5) M 1.55 1 Dimenswoning and (o‘erancing per ASME v14 SM 850 Basic Dimenswon. Theoreucauy exact value shown wnnout to‘erances. Mlcrucmp Technolagy Drawmg No 604-2057A
2011-2018 Microchip Technology Inc. DS20005010G-page 40
MCP7940N
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2011-2018 Microchip Technology Inc. DS20005010G-page 41
MCP7940N
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 A1 18
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D
N
E
E1
NOTE 1
12
b
e
c
A
A1
A2
L1 L
φ
  & ?J>
8-Lead Plastic Thin Shrink Small Outline (ST) - 4.4 mm Body [TSSOP] C1 \ LL SiLK SCREEN RECOMMENDED LAND PATTERN Units MiLLIMETERS Dimension Limits MN | NOM i MAX Contact Pitch E o 55 BSC Contact Pad Spaclng c1 5 90 Conlact Pad Width (X5) X1 0 45 Canlact Pad Length (XS) vi 1 45 Distance Between Pads <3 0.20="" mates.="" 1="" dimensiomng="" and="" iolerancing="" perasme="" y14.5m="" bsc="" basic="" dimension.="" theoreticaily="" exact="" vaiue="" snown="" wimoui="" ioierances.="" micmchip="" technaiogy="" drawing="" no="" cda-zobea="">
2011-2018 Microchip Technology Inc. DS20005010G-page 42
MCP7940N
Note: For the most current package drawings, please see the Microchip Packaging Specification located at
http://www.microchip.com/packaging
8-Lead Plastic Micro Small Outline Package (MS) [MSOP] E‘lIZ @0100 f 1 SEATING PLANE J SIDE VIEW A1 * fl/ SEE DETAlLC _ \—g 7 J END VIEW Microcmp Technology Drawmg 00471111: Sheet 1 012 2011-2015 Mlcrucmp Technology lm:
2011-2018 Microchip Technology Inc. DS20005010G-page 43
MCP7940N
Note: For the most current package drawings, please see the Microchip Packaging Specification located at
http://www.microchip.com/packaging
8-Lead Plastic Micro Small Outline Package (MS) [MSOF] SEATING PLANE (Ll) DETAIL c Unlts MILLlMETERS Dlmension lells MIN NOM MAX Number oi Plns N | a l Pitch e 0.65 380 Overall Heighl A - - 1.10 Molded Package Thickness A2 0 75 0.85 0.95 Standoff Al 0 00 - 0.15 Overall Wldlh E 4 90 BSC Molded Package Wldlh El 3 00 580 Overall Length D 3 00 550 Foot Length L 0 40 | 0 50 l 0 00 Footprint L1 0 95 REF Fool Angle W 0° - 5° Lead Thickness c 0 DB - 0 23 Lead width o 0 22 - 0 40 Notes: l Pin 1 visual index teature may vary. bul musl be located Within the hatched area 2 Dimenslons 0 and El do not include rnold llash or protrusions. Mold flash or protrusions shall not exceed 0 15mm per side 3 Dimehsrohrng and tolerahcrng oer ASME v14 5M asc: aaslc Dlmension. Theoretlcally exact value shown without tolerances. REF: Reterence Dlrnenslon. usually without tolerance, tor intorrnation purposes only. Mlcrochlo Technology Drawlng 00471110 Sheet 2 otz 2011-2018 Ml
2011-2018 Microchip Technology Inc. DS20005010G-page 44
MCP7940N
Note: For the most current package drawings, please see the Microchip Packaging Specification located at
http://www.microchip.com/packaging
S-Lead Plastic Micro Small Outline Package (MS) [MSOP] ’* ” ' \ SILK SCREEN I t _»——GX RECOMMENDED LAND PATTERN Units MILLIMETERS Dimension Limits MW \ NOM \ MAX Contact Pitch E o 65 589 Contact Pad Spacing c A 40 Oveiaii Width Z 5 35 Contact Pad Width (xa) x1 0.45 Contact Pad Length (xa) Y1 1.45 Distance Between Pads G1 2.95 Distance Between Pads GX 0.20 Notes 1 Dimensiuning and tolerancing perASME Y14 5M BSC. Bast: Dimension. TheoreticaHy exact vatue shown wilhout tolerances. Microchip Technoicgy Drawing No C0472111A
2011-2018 Microchip Technology Inc. DS20005010G-page 45
MCP7940N
Note: For the most current package drawings, please see the Microchip Packaging Specification located at
http://www.microchip.com/packaging
8-Lead Plastic Dual Flat, No Lead Package (MN) — 2x3x0.75mm Body [TDFN] E N x ! ‘ m. {ESQ ’ \\\\ \ \v \\\\ \\\\\ 2x Q 0.15 c \\\\\\\\} 1 2‘ 2X 5- 0 TOP VIEW // 0.10 c A SEAT‘NG PLANE MT ‘— A3 SIDE V‘EW <—d2—— exposzo="" j="" pm="" 8xb4="">‘ \ New o1o® CA‘B‘ o 05® C BO'I'FOM VIEW chmcmp Technology Drawing No couzgc
2011-2018 Microchip Technology Inc. DS20005010G-page 46
MCP7940N
Note: For the most current package drawings, please see the Microchip Packaging Specification located at
http://www.microchip.com/packaging
8-Lead Plastic Dual Flat, No Lead Package (MN) — 2x3x0.75mm Body [TDFN] NOTEZ Units MILLIMETERS Dxmensxon Limits MIN \ NOM | MAX Number of Plns N 8 Pitch e 0.50 BSC Overaii Hewght A 0.70 0.75 0.80 Standoff A1 0.00 0.02 0.05 Contact Thickness A3 0.20 REF OveraH Length D 2 00 BSC Overaii Wwdth E 3.00 BSC Exposed Pad Length D2 1.20 , 1.60 Exposed Pad Width E2 1.20 - 1.50 Contact Width [3 0.20 0.25 0.30 Contact Length L 0 25 0 30 0 45 Contact-lo-Exposed Pad K 0.20 - - Notes: 1. Pin 1 visual \ndex ieature may vary, but must be located thhm the hatched area. 2. Package may have one or more exposed tie bars at ends 3. Package is saw smguiated 4. Dwmensiuning and ioierancing perASME V14.5M 580' Base Dwmenslon TheorehcaHy exact value shown wwihout tolerances REF: Reference Dimension, usuaHy wwlhout tolerance, for miormation purposes omy. Mlcrochwp Technology Drawmg N0. CO4-129C Sheet 2 of 2
2011-2018 Microchip Technology Inc. DS20005010G-page 47
MCP7940N
Note: For the most current package drawings, please see the Microchip Packaging Specification located at
http://www.microchip.com/packaging
‘— W2 —’ stLK SCREEN I:IT WT’HU D D71 X. 4‘ L ——E<— recommended="" land="" pattern="" umts="" mtllimeters="" dlmenston="" ltmtls="" min="" |="" nom="" |="" max="" suntan="" fttch="" e="" u="" 50="" bsc="" optianat="" center="" pad="" wtdlh="" w2="" 1.45="" optionat="" center="" pad="" length="" t2="" 1.35="" contact="" pad="" spacing="" c1="" 3.00="" contact="" pad="" wtdlh="" (x8)="" x1="" 0="" 30="" comm="" pad="" length="" (x3)="" v1="" 0="" 75="" dtstance="" between="" pads="" s="" 0.20="" notes="" 1="" dtmenstonlng="" and="" tolerancmg="" perasme="" v14="" sm="" 550="" east:="" dtmenston="" thealeucatly="" exact="" value="" shown="" withom="" |0\elances.="" mtcrucmp="" teehnotngy="" drawmg="" no="" 004-2128a="">
2011-2018 Microchip Technology Inc. DS20005010G-page 48
MCP7940N
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2011-2018 Microchip Technology Inc. DS20005010G-page 49
MCP7940N
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< !""%81%#%!%)"#""%)"#"""6%1U"%
 !"%8=1;
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& !"#$%&"'""($)%
*++&&&!!+$
@" E?K8
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E#!7)(" E 
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%%($$""  11; 1< 1;
>"( 1 1; L L
#%#%N% 8  <1 <;
%%($N% 81  ; 
G3A  < <J; 
( A 11; 1< 1;
A%$""   1 1;
@A%N% 71  J 
A&A%N% 7 1 1 
G3&R > L L <
N
E1
NOTE 1
D
123
A
A1
A2
L
b1
b
e
E
eB
c
  & ?1>
2011-2018 Microchip Technology Inc. DS20005010G-page 50
MCP7940N
APPENDIX A: REVISION HISTORY
Revision A (04/2011)
Original release of this document.
Revision B (09/2011)
Added Figure 1-2
Added Parameter D15 to Table 1-1
Added Section 3.3 “Oscillator Input/Output
(X1, X2)”, Section 3.4 “Multifunction Pin
(MFP)”, Section 3.5 “Backup Supply (Vbat)”
Added Figure 5-1
Updated Section 5.2.3 “Oscillator Failure Sta-
tus”, Section 5.2.4 “Crystal Specs”,
Section 5.2.5 “Power-fail Time-stamp”.
Revision C (12/2011)
Added DC/AC Char. Charts.
Revision D (11/2012)
Added Extended Temp.
Revision E (01/2013)
Revised Table 1-2: AC Characteristics; temperature
range
Revision F (03/2014)
Updated overall content for improved clarity. Added
detailed descriptions of registers. Updated block dia-
gram and application schematic.
Defined names for all bits and registers, and renamed
the bits shown in Table 7-1 for clarification.
Renamed the DC characteristics shown in Table 7-2
for clarification.
TABLE 7-1: BIT NAME CHANGES
TABLE 7-2: DC CHARACTERISTIC NAME CHANGES
Revision G (07/2018)
Updated Section 5.5.1 “Square Wave Output Mode”.
Old Bit Name New Bit Name
OSCON OSCRUN
VBAT PWRFAIL
LP LPYR
SQWE SQWEN
ALM0 ALM0EN
ALM1 ALM1EN
RS0 SQWFS0
RS1 SQWFS1
RS2 CRSTRIM
CALIBRATION TRIMVAL<6:0>
ALM0POL ALMPOL
ALM1POL ALMPOL
ALM0C<2:0> ALM0MSK<2:0>
ALM1C<2:0> ALM1MSK<2:0>
Old Name Old Symbol New Name New Symbol
Operating current SRAM ICC Read SRAM/RTCC register operating current ICCREAD
ICC Write ICCWRITE
Operating current IVCC Timekeeping current ICCT
IBAT Timekeeping backup current IBATT
Standby current ICCS VCC data retention current (oscillator off) ICCDAT
2011-2018 Microchip Technology Inc. DS20005010G-page 51
MCP7940N
THE MICROCHIP WEBSITE
Microchip provides online support via our WWW site at
www.microchip.com. This website is used as a means
to make files and information easily available to
customers. Accessible by using your favorite Internet
browser, the website contains the following
information:
Product Support – Data sheets and errata,
application notes and sample programs, design
resources, user’s guides and hardware support
documents, latest software releases and archived
software
General Technical Support – Frequently Asked
Questions (FAQ), technical support requests,
online discussion groups, Microchip consultant
program member listing
Business of Microchip – Product selector and
ordering guides, latest Microchip press releases,
listing of seminars and events, listings of
Microchip sales offices, distributors and factory
representatives
CUSTOMER CHANGE NOTIFICATION
SERVICE
Microchip’s customer notification service helps keep
customers current on Microchip products. Subscribers
will receive e-mail notification whenever there are
changes, updates, revisions or errata related to a
specified product family or development tool of interest.
To register, access the Microchip website at
www.microchip.com. Under “Support”, click on
“Customer Change Notification” and follow the
registration instructions.
CUSTOMER SUPPORT
Users of Microchip products can receive assistance
through several channels:
Distributor or Representative
Local Sales Office
Field Application Engineer (FAE)
Technical Support
Customers should contact their distributor,
representative or Field Application Engineer (FAE) for
support. Local sales offices are also available to help
customers. A listing of sales offices and locations is
included in the back of this document.
Technical support is available through the website
at: http://microchip.com/support
RT 44x
2011-2018 Microchip Technology Inc. DS20005010G-page 52
MCP7940N
PRODUCT IDENTIFICATION SYSTEM
To order or obtain information, e.g., on pricing or delivery, refer to the factory or the listed sales office. Not every possible ordering
combination is listed below.
PART NO. X /XX
PackageTemperature
Range
Device
Device: MCP7940N = 1.8V - 5.5V I2C Serial RTCC
MCP7940NT= 1.8V - 5.5V I2C Serial RTCC
(Tape and Reel)
Temperature
Range:
I = -40°C to +85°C
E = -40°C to +125°C
Package: SN = 8-Lead Plastic Small Outline (3.90 mm body)
ST = 8-Lead Plastic Thin Shrink Small Outline
(4.4 mm body, I-temp only)
MS = 8-Lead Plastic Micro Small Outline
MNY(1) = 8-Lead Plastic Dual Flat, No Lead (I-temp only)
P = 8-Lead Plastic PDIP (300 mil body, I-temp only)
Examples:
a) MCP7940N-I/SN: Industrial Temperature,
SOIC package.
b) MCP7940NT-I/SN: Industrial Temperature,
SOIC package, Tape and Reel.
c) MCP7940NT-I/MNY: Industrial Tempera-
ture, TDFN package, Tape and Reel.
d) MCP7940N-I/P: Industrial Temperature,
PDIP package.
e) MCP7940N-E/MS: Extended Temperature,
MSOP package.
f) MCP7940NT-E/MS: Extended Temperature,
MSOP package, Tape and Reel.
g) MCP7940NT-I/ST: Industrial Temperature,
TSSOP package, Tape and Reel.
h) MCP7940NT-E/SN: Extended Temperature,
SOIC package, Tape and Reel.
Note 1: "Y" indicates a Nickel Palladium Gold (NiPdAu) finish.
QUALITY MANAGEMENT SYSTEM CERTIFIED BY DNV = ISO/TS 16949=
2011-2018 Microchip Technology Inc. DS20005010G-page 53
Information contained in this publication regarding device
applications and the like is provided only for your convenience
and may be superseded by updates. It is your responsibility to
ensure that your application meets with your specifications.
MICROCHIP MAKES NO REPRESENTATIONS OR
WARRANTIES OF ANY KIND WHETHER EXPRESS OR
IMPLIED, WRITTEN OR ORAL, STATUTORY OR
OTHERWISE, RELATED TO THE INFORMATION,
INCLUDING BUT NOT LIMITED TO ITS CONDITION,
QUALITY, PERFORMANCE, MERCHANTABILITY OR
FITNESS FOR PURPOSE. Microchip disclaims all liability
arising from this information and its use. Use of Microchip
devices in life support and/or safety applications is entirely at
the buyer’s risk, and the buyer agrees to defend, indemnify and
hold harmless Microchip from any and all damages, claims,
suits, or expenses resulting from such use. No licenses are
conveyed, implicitly or otherwise, under any Microchip
intellectual property rights unless otherwise stated.
Trademarks
The Microchip name and logo, the Microchip logo, AnyRate, AVR,
AVR logo, AVR Freaks, BitCloud, chipKIT, chipKIT logo,
CryptoMemory, CryptoRF, dsPIC, FlashFlex, flexPWR, Heldo,
JukeBlox, KeeLoq, Kleer, LANCheck, LINK MD, maXStylus,
maXTouch, MediaLB, megaAVR, MOST, MOST logo, MPLAB,
OptoLyzer, PIC, picoPower, PICSTART, PIC32 logo, Prochip
Designer, QTouch, SAM-BA, SpyNIC, SST, SST Logo,
SuperFlash, tinyAVR, UNI/O, and XMEGA are registered
trademarks of Microchip Technology Incorporated in the U.S.A.
and other countries.
ClockWorks, The Embedded Control Solutions Company,
EtherSynch, Hyper Speed Control, HyperLight Load, IntelliMOS,
mTouch, Precision Edge, and Quiet-Wire are registered
trademarks of Microchip Technology Incorporated in the U.S.A.
Adjacent Key Suppression, AKS, Analog-for-the-Digital Age, Any
Capacitor, AnyIn, AnyOut, BodyCom, CodeGuard,
CryptoAuthentication, CryptoAutomotive, CryptoCompanion,
CryptoController, dsPICDEM, dsPICDEM.net, Dynamic Average
Matching, DAM, ECAN, EtherGREEN, In-Circuit Serial
Programming, ICSP, INICnet, Inter-Chip Connectivity,
JitterBlocker, KleerNet, KleerNet logo, memBrain, Mindi, MiWi,
motorBench, MPASM, MPF, MPLAB Certified logo, MPLIB,
MPLINK, MultiTRAK, NetDetach, Omniscient Code Generation,
PICDEM, PICDEM.net, PICkit, PICtail, PowerSmart, PureSilicon,
QMatrix, REAL ICE, Ripple Blocker, SAM-ICE, Serial Quad I/O,
SMART-I.S., SQI, SuperSwitcher, SuperSwitcher II, Total
Endurance, TSHARC, USBCheck, VariSense, ViewSpan,
WiperLock, Wireless DNA, and ZENA are trademarks of
Microchip Technology Incorporated in the U.S.A. and other
countries.
SQTP is a service mark of Microchip Technology Incorporated in
the U.S.A.
Silicon Storage Technology is a registered trademark of
Microchip Technology Inc. in other countries.
GestIC is a registered trademark of Microchip Technology
Germany II GmbH & Co. KG, a subsidiary of Microchip
Technology Inc., in other countries.
All other trademarks mentioned herein are property of their
respective companies.
© 2018, Microchip Technology Incorporated, All Rights
Reserved.
ISBN: 978-1-5224-3350-7
Note the following details of the code protection feature on Microchip devices:
Microchip products meet the specification contained in their particular Microchip Data Sheet.
Microchip believes that its family of products is one of the most secure families of its kind on the market today, when used in the
intended manner and under normal conditions.
There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our
knowledge, require using the Microchip products in a manner outside the operating specifications contained in Microchip’s Data
Sheets. Most likely, the person doing so is engaged in theft of intellectual property.
Microchip is willing to work with the customer who is concerned about the integrity of their code.
Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not
mean that we are guaranteeing the product as “unbreakable.”
Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of our
products. Attempts to break Microchip’s code protection feature may be a violation of the Digital Millennium Copyright Act. If such acts
allow unauthorized access to your software or other copyrighted work, you may have a right to sue for relief under that Act.
Microchip received ISO/TS-16949:2009 certification for its worldwide
headquarters, design and wafer fabrication facilities in Chandler and
Tempe, Arizona; Gresham, Oregon and design centers in California
and India. The Company’s quality system processes and procedures
are for its PIC® MCUs and dsPIC® DSCs, KEELOQ® code hopping
devices, Serial EEPROMs, microperipherals, nonvolatile memory and
analog products. In addition, Microchip’s quality system for the design
and manufacture of development systems is ISO 9001:2000 certified.
6‘ MICROCHIP AMERICAS ASIA/PACIFIC ASIA/PACIFIC EUROPE
2011-2018 Microchip Technology Inc. DS20005010G-page 54
AMERICAS
Corporate Office
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Chandler, AZ 85224-6199
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Worldwide Sales and Service
10/25/17

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