DS17885/DS17887

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REGISTER B

MSB

LSB

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

SET

PIE

AIE

UIE

SQWE

DM

24/12

DSE

SET – When the SET bit is a 0, the update transfer functions normally by advancing the counts once per

second. When the SET bit is written to a 1, any update transfer is inhibited and the program can initialize

the time and calendar bytes without an update occurring in the midst of initializing. Read cycles can be

executed in a similar manner. SET is a read/write bit that is not modified by internal functions of the

DS17885/DS17887.

PIE – Periodic Interrupt Enable. The PIE bit is a read/write bit, which allows the periodic interrupt flag

periodic rate. PIE is not modified by any internal DS17885/DS17887 functions.

AIE – Alarm Interrupt Enable. The AIE bit is a read/write bit which, when set to a 1, permits the alarm

bytes equal the three alarm bytes, including a “don’t care” alarm code of binary 11XXXXXX. When the

DS17885/DS17887 do not affect the AIE bit.

UIE – Update-Ended Interrupt Enable. The UIE bit is a read/write bit that enables the update-end flag

SQWE – Square-Wave Enable. When the SQWE bit is set to a 1 and E32k = 0, a square-wave signal at

the frequency set by the rate-selection bits RS3 through RS0 is driven out on the SQW pin. When the

SQWE bit is set to 0and E32k = 0, the SQW pin is held low. SQWE is a read/write bit. SQWE is set to a

DM – Data Mode. The DM bit indicates whether time and calendar information is in binary or BCD

format. The DM bit is set by the program to the appropriate format and can be read as required. This bit is

not modified by internal functions. A 1 in DM signifies binary data while a 0 in DM specifies BCD data.

24/12 – 24/12-Control Bit. This bit establishes the format of the hours byte. A 1 indicates the 24-hour

mode and a 0 indicates the 12-hour mode. This bit is read/write.

DSE – Daylight Savings Enable. The DSE bit is a read/write bit that enables two special updates when

DSE is set to 1. On the first Sunday in April, the time increments from 1:59:59 AM to 3:00:00 AM. On

the last Sunday in October, when the time first reaches 1:59:59 AM, it changes to 1:00:00 AM. These

special updates do not occur when the DSE bit is a 0. This bit is not affected by internal functions.