Datasheet

DS1685/DS1687 3V/5V Real-Time Clocks
17 of 34
Figure 4. Update-Ended And Periodic-Interrupt Relationship
EXTENDED FUNCTIONS
The extended functions provided by the DS1685/DS1687 that are new to the RAMified RTC family are accessed by
a software-controlled bank-switching scheme, as illustrated in Figure 5. 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 DS1685/DS1687 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.
t
PI
= PERIODIC INTERRUPT TIME INTERNAL PER TABLE 3.
t
BUC
= DELAY BEFORE UPDATE CYCLE = 244µs.
UIP
UF
PF
1 second
t
PI
t
PI/2
t
BUC
t
PI/2