MCP79400 datasheet(11/42 Pages) MICROCHIP

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 2011 Microchip Technology Inc.

DS25009C-page 11

MCP7940X

5.0

RTCC FUNCTIONALITY

The MCP7940X 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. An

integrated VCC switch enables the device to maintain

the time and date and also the contents of the SRAM

during a VCC power failure.

5.1

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. All SRAM locations are

battery-backed-up during a VCC power fail. Unused

locations are not accessible, MCP7940X 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 5-1. 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 writing to 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 insuring 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, Calibration and ID Unlock registers.

• 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-0x17h are the same as 0x0Bh-

0x11h but are used for Alarm 1.

• Addresses 0x18h-0x1Fh are used for the time-

stamp feature.

The detailed memory map is shown in Table 5-1.

FIGURE 5-1:

MEMORY MAP

0x00

0x06

Time and Date

Configuration and Calibration

Alarm 0

Alarm 1

Time-Stamp

SRAM (64 Bytes)

0x07

0x09

0x0A

0x10

0x11

0x17

0x18

0x1F

0x20

0x5F

0x60

0xFF

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