MCP79400 datasheet(14/42 Pages) MICROCHIP

14 / 42 page

MCP7940X

DS25009C-page 14

 2011 Microchip Technology Inc.

is cleared in software.

• ALMxC2:0: These Configuration bits determine

the alarm match. The logic will trigger the alarm

based on one of the following match conditions:

• The 12/24-hour bits 0xCh.6 and 0x13h.6 are cop-

ies of the bit in 0x02h.6. The bits are read-only.

0x18h-0x1Bh are used for the timesaver function.

These registers are loaded at the time when VCC fails

and the RTCC operates on the VBAT. The VBAT bit is

also set at this time. These registers are cleared when

the VBAT bit is cleared in software.

0x1Ch-0x1Fh are used for the timesaver function.

These registers are loaded at the time when VCC is

restored and the RTCC switches to VDD. These

registers are cleared when the VBAT bit is cleared in

software.

5.2

FEATURES

5.2.1

UNLOCK SEQUENCE

The unique ID location is user accessible by using the

unlock ID sequence.

The unique ID location is 64-bits (8 bytes) and is

stored in EEPROM locations 0xF0 to 0xF7. This

location can be read at any time, however, a write is

inhibited until unlocked.

To unlock the write access to this location the following

sequence must be completed:

• A single write of 0x55h to address 0x09. Stop

• A single write of 0xAAh to address 0x09. Stop

This will allow the unique EEPROM locations to be

written.

After the byte or page write to these locations, the

write sequence is initiated by the Stop condition. At

this time, the ID locations are locked and no further

writes are possible to this location unless a complete

unlock sequence is repeated.

000 – Seconds match

001 – Minutes match

010 – Hours match (takes into account 12/24

hour)

011 – Matches the current day, interrupt at

12.00.00 a.m. Example: 12 midnight on

100

–Date

101

– RESERVED

110

– RESERVED

111

– Seconds, Minutes, Hour, Day, Date,

Month

Note:

It is strongly recommended that the

timesaver function only be used when the

oscillator is running. This will ensure

accurate functionality.

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