Datasheet
MCP7940N
DS20005010F-page 8 2010-2014 Microchip Technology Inc.
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 V
CC (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 V
CC
is unavailable.
If the battery backup feature is not being used, the
V
BAT 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
V
BAT 33333Battery Backup Supply Input
Vss 44444Ground
SDA 55555Bidirectional Serial Data (I
2
C™)
SCL 66666Serial Clock (I
2
C)
MFP 77777Multifunction Pin
Vcc 88888Primary Power Supply
Note: Exposed pad on TFDN can be connected to Vss or left floating.