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Rev. 5.00, 09/03, page 423 of 760
13.3.3 Reading the Time
Figure 13.3 shows how to read the time. If a carry occurs while reading the time, the correct time
will not be obtained, so it must be read again. Part (a) in figure 13.3 shows the method of reading
the time without using interrupts; part (b) in figure 13.3 shows the method using carry interrupts.
To keep programming simple, method (a) should normally be used.
Write 0 to CF in RCR1
Note: Set AF to 1 so that alarm
flag is not cleared.
Clear CIE in RCR1 to 0
Read RCR1 and check CF
Write 0 to CIE in RCR1
Carry flag = 1?
No
Yes
Clear the carry flag
Disable the carry
interrupt
Read counter
register
Write 1 to CIE in RCR1,
and write 0 to CF in RCR1
Note: Set AF in RCR1 to 1 so that
alarm flag is not cleared.
Interrupt
generated?
No
Yes
Enable the carry
interrupt
Clear the carry flag
Disable the carry
interrupt
Read counter
register
To read the time
without using interrupts
b. To use interrupts
a.
Figure 13.3 Reading the Time