Toshiba TMP91C815F Data Book page 210

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Readout of timer data that used /ALARM output
Timer data can be read with rising edge of /ALARM output by detecting /ALARM='1' with interrupt routine of
INTRTC of 1 Hz
/ALARM
Internal INTRTC
The reason why read a timer of RTC after reading PORT in interrupt routine of /ALARM=1 is that carry of
RTC timer occurs with rising edge of pulse period of 1 Hz. By reading timer during 0.5second after carry
happening, right data (a timer value) can be read.
Figuire3.11(3) Read out of the timer table used /ALARM output
START
RESTR<DIS1HZ>='0',
RESTR<DIS16HZ>='1',
PAGER<ENAALM>='0'
Enable 1Hz output
INTRTC?
(1Hz)
YES
/ALARM=1?
YES
Read the timer data
END
0.5 second
Interrupt routine
91C815-
207
NO
NO
(note):
This period is within
0.5 second.
Read /ALARM="1"
TMP91C815