DS1689 Datasheet, PDF (15/32 Pages) Dallas Semiconductor – 3-Volt/5-Volt Serialized Real-Time Clock with NV RAM Control

DS1689/DS1693
EXTENDED FUNCTIONS
The extended functions provided by the DS1689/DS1693 that are new to the RAMified RTC family are
accessed via a software controlled bank switching scheme, as illustrated in Figure 4. In bank 0, the
clock/calendar registers and 50 bytes of user RAM are in the same locations as for the DS1287. As a
result, existing routines implemented within BIOS, DOS, or application software packages can gain
access to the DS1689/DS1693 clock registers with no changes. Also in bank 0, an extra 64 bytes of RAM
are provided at addresses just above the original locations for a total of 114 directly addressable bytes of
user RAM.
When bank 1 is selected, the clock/calendar registers and the original 50 bytes of user RAM still appear
as bank 0. However, the Dallas registers which provide control and status for the extended functions will
be accessed in place of the additional 64 bytes of user RAM. The major extended functions controlled by
the Dallas registers are listed below:
1. Silicon Revision byte
2. Serial Number
3. 8-Byte Customer Specific ROM or Serial Number
4. Century counter
5. Auxiliary Battery Control/Status
6. Wake-Up
7. Kickstart
8. RAM Clear Control/Status
9. V_CC Powered Elapsed Time Counter
10. V_BAT Powered Elapsed Time Counter
11. Power-on Cycle Counter
The bank selection is controlled by the state of the DV0 bit in register A. To access bank 0 the DV0 bit
should be written to a 0. To access bank 1, DV0 should be written to a 1. Register locations designated as
reserved in the bank 1 map are reserved for future use by Dallas Semiconductor. Bits in these locations
cannot be written and will return a 0 if read.
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