Datasheet

MCP7941X
DS22266A-page 12 Preliminary  2010 Microchip Technology Inc.
• 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 V
CC fails
and the RTCC operates on the V
BAT. 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 V
CC is
restored and the RTCC switches to V
DD. These
registers are cleared when the V
BAT 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.