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Real time clock with ST7 Timer Output Compare

These four counters are coded on one byte each and are updated by the Output Compare 1

interrupt routine as shown in Figure 2.

Figure 2. Software Counter Update Flowchart

OC1 INTERRUPT

UPDATE

OCxHR AND OCxLR

REGISTER

INCREMENT 100ms COUNTER

100ms CNT

= 10 ?

RESET 100ms COUNTER

INCREMENT SECOND

COUNTER

SECOND CNT

= 60 ?

yes

yes

RESET SECOND

COUNTER

INCREMENT MINUTE

COUNTER

MINUTE CNT

= 60 ?

yes

RESET MINUTE

COUNTER

INCREMENT HOUR

COUNTER

no

no

no

HOUR CNT

= 24 ?

no

yes

RESET HOUR

COUNTER