Datasheet

2012 Microchip Technology Inc. Preliminary DS22292A-page 9
MCP7940M
4.0 RTCC FUNCTIONALITY
The MCP7940M family is a highly integrated RTCC.
On-board time and date counters are driven from a low-
power oscillator to maintain the time and date.
4.1 RTCC MEMORY MAP
The RTCC registers are contained in addresses
0x00h-0x1fh. 64 bytes of user-accessable SRAM are
located in the address range 0x20-0x5f. The SRAM
memory is a separate block from the RTCC control
and Configuration registers. Unused locations are not
accessible, MCP7940M will noACK after the address
byte if the address is out of range, as shown in the
shaded region of the memory map in Figure 4-1. The
shaded areas are not implemented and read as ‘0’. No
error checking is provided when loading time and date
registers.
Addresses 0x00h-0x06h are the RTCC Time and
Date registers. These are read/write registers.
Care must be taken when accessing these regis-
ters while the oscillator is running.
Incorrect data can appear in the Time and Date
registers if a write is attempted during the time
frame where these internal registers are being
incremented. The user can minimize the likeli-
hood of data corruption by ensuring that any
writes to the Time and Date registers occur before
the contents of the second register reach a value
of 0x59H.
Addresses 0x07h-0x09h are the device Configu-
ration and Calibration.
Addresses 0x0Ah-0x10h are the Alarm 0 regis-
ters. These are used to set up the Alarm 0, the
Interrupt polarity and the Alarm 0 compare.
Addresses 0x11h-0x16h are the same as 0x0Bh-
0x11h but are used for Alarm 1.
Addresses 0x17h-0x1Fh are reserved for future
use and should not be used.
The detailed memory map is shown in Tab l e 4- 1.
FIGURE 4-1: MEMORY MAP
0x00
0x06
Time and Date
Configuration and Calibration
Alarm 0
Alarm 1
Reserved do not Use
SRAM (64 Bytes)
0x07
0x09
0x0A
0x10
0x11
0x16
0x17
0x1F
0x20
0x5F
0x60
0xFF