DS1689 Datasheet, PDF (6/32 Pages) Dallas Semiconductor – 3-Volt/5-Volt Serialized Real-Time Clock with NV RAM Control

DS1689/DS1693
When 5-volt operation is selected, the device is fully accessible and data can be written and read only
when V_CCI is greater than 4.5 volts. When V_CCI is below 4.5 volts, read and writes are inhibited. However,
the timekeeping function continues unaffected by the lower input voltage. As V_CC falls below the greater
of V_BAT and V_BAUX, the RAM and timekeeper are switched over to a lithium battery connected either to
the V_BAT pin or V_BAUX pin.
When 3-volt operation is selected and applied within normal limits, the device is fully accessible and data
can be written or read. When V_CCI falls below V_PF, access to the device is inhibited. If V_PF is less than
V_BAT and V_BAUX, the power supply is switched from V_CCI to the backup supply (the greater of V_BAT and
V_BAUX) when V_CCI drops below V_PF. If V_PF is greater than V_BAT and V_BAUX, the power supply is switched
from V_CCI to the backup supply when V_CCI drops below the larger of V_BAT and V_BAUX.
When V_CC falls below V_PF, the chip is write-protected. With the possible exception of the KS , PWR , and
SQW pins, all inputs are ignored and all outputs are in a high impedance state.
RTC ADDRESS MAP
The address map for the RTC registers of the DS1689/DS1693 is shown in Figure 2. The address map
consists of the 14-clock/calendar registers. Ten registers contain the time, calendar, and alarm data, and
four bytes are used for control and status. All registers can be directly written or read except for the
following:
1. Registers C and D are read-only.
2. Bit 7 of Register A is read-only.
3. The high order bit of the seconds byte is read-only.
DS1689 REAL TIME CLOCK ADDRESS MAP Figure 2
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