DS1689 Datasheet, PDF (12/32 Pages) Dallas Semiconductor – 3-Volt/5-Volt Serialized Real-Time Clock with NV RAM Control

REGISTER A
MSB
BIT 7
BIT 6
UIP
DV2
BIT 5
DV1
BIT 4
DV0
BIT 3
RS3
BIT 2
RS2
DS1689/DS1693
BIT 1
RS1
LSB
BIT 0
RS0
UIP - The Update In Progress (UIP) bit is a status flag that can be monitored. When the UIP bit is a 1, the
update transfer will soon occur. When UIP is a 0, the update transfer will not occur for at least 244 ms.
The time, calendar, and alarm information in RAM is fully available for access when the UIP bit is 0. The
UIP bit is read-only. Writing the SET bit in Register B to a one inhibits any update transfer and clears the
UIP status bit.
DV0, DV1, DV2 - These bits are defined as follows:
DV2 =
Countdown Chain
1 - resets countdown chain only if DV1=1
0 - countdown chain enabled
DV1 =
Oscillator Enable
0 - oscillator off
1 - oscillator on
DV0 =
Bank Select
0 - original bank
1 - extended registers
A pattern of 01X is the only combination of bits that will turn the oscillator on and allow the RTC to keep
time. A pattern of 11X will enable the oscillator but holds the countdown chain in reset. The next update
will occur at 500 ms after a pattern of 01X is written to DV2, DV1, and DV0.
RS3, RS2, RS1, RS0 - These four rate-selection bits select one of the 13 taps on the 15-stage divider or
disable the divider output. The tap selected can be used to generate an output square wave (SQW pin)
and/or a periodic interrupt. The user can do one of the following:
Enable the interrupt with the PIE bit;
Enable the SQW output pin with the SQWE bit;
Enable both at the same time and the same rate; or
Enable neither.
Table 2 lists the periodic interrupt rates and the square wave frequencies that can be chosen with the RS
bits.
12 of 32