DS1689/DS1693

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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

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 0. To access bank 1, DV0 should be written to 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 return a 0 if read.