Rainbow Electronics DS1687 - Manual (Page 13)

DS1685/DS1687
13 of 38
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
DS1685/DS1687.
PIE – The periodic-interrupt enable bit is a read/write bit that allows the periodic-interrupt flag (PF) bit in
Register C to drive the
IRQ pin low. When the PIE bit is set to 1, periodic interrupts are generated by
driving the IRQ pin low at a rate specified by the RS3–RS0 bits of Register A. A 0 in the PIE bit blocks
the IRQ output from being driven by a periodic interrupt, but the periodic flag (PF) bit is still set at the
periodic rate. PIE is not modified by any internal DS1685/DS1687 functions.
AIE – The alarm-interrupt enable (AIE) bit is a read/write bit which, when set to a 1, permits the alarm
flag (AF) bit in Register C to assert
IRQ . An alarm interrupt occurs for each second that the three time
bytes equal the three alarm bytes, including a “don’t care” alarm code of binary 11XXXXXX. When the
AIE bit is set to 0, the AF bit does not initiate the
IRQ signal. The internal functions of the
DS1685/DS1687 do not affect the AIE bit.
UIE – The update-ended interrupt-enable (UIE) bit is a read/write bit that enables the update-end flag
(UF) bit in Register C to assert
IRQ . The SET bit going high clears the UIE bit.
SQWE – When the square-wave enable (SQWE) bit is set to a 1 and E32K = 0, a square-wave signal at
the frequency set by the rate-selection bits RS3–RS0 is driven out on the SQW pin. When the SQWE bit
is set to 0 and E32K = 0, the SQW pin is held low. SQWE is a read/write bit.
DM – The data mode (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 – The 24/12 control 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 – The Daylight Savings Enable (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.