MCP79411 datasheet(13/38 Pages) MICROCHIP

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 2011 Microchip Technology Inc.

Preliminary

DS22266B-page 13

MCP7941X

• 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.

4.2

FEATURES

4.2.1

STATUS REGISTER

The STATUS register is in the nonvolatile EEPROM

array. To access the STATUS register, the address of

0xFFh is written to and read from. ACK polling may be

used to determine if the write is complete. The bits in

this register are defined as:

• Bit 3:2 are the EEPROM array block protection

bits. These bits are in the nonvolatile EEPROM

array. This allows protection of the following

areas:

- 00 – None of the array is protected.

- 01 – The upper 1/4 of the array 0x60h-0x7fh

is protected.

- 10 – The upper 1/2 of the array 0x40h-0x7fh

is protected.

- 11 – All of the array 0x00-0x7fh is protected.

• The unused bits are reserved at this time and

read as ‘0’.

• With the current address read operation, the

address is not incremented. Consequently, the

subsequent reads are done from the same

location.

If multiple bytes are loaded to the STATUS register,

only the last byte is written.

4.2.2

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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