Xycom XVME-113, User Manual

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Chapter 3 – Real Time Clock
3-12
3.5.2.2
Setting Registers with the RTC Running
If only one or a few of the date and time registers need to be set, they can be set while the RTC is running. The algorithm
is more complicated, involving verification of the write operations by checking the CF. The procedure for setting the
RTC time while it is running is described in the flow chart and instructions below.
•
••••••••••••••••••••••
•
•••••••••••••••••••••••••••••
• • Clear CF • Clear the Carry Flag in Control Register A.
• •••••••••••••••••••••••••••••
• •
• •••••••••••••••••••••••••••••
• • Write to Counter Register •
• •••••••••••••••••••••••••••••
• •
• •••••••••••••••••••••••••••••
• YES • Verify Write Operation • Poll CF bit in Control Register A.
•••••••• (CF = 1 ?) •
•••••••••••••••••••••••••••••
• NO
•
(Repeat for each register to be set)
Follow the procedure below to set the RTC time with the clock running:
1. Clear the CF bit in Control Register A to '0'. Note: To prevent the AF bit from being cleared as well,
set the AF bit to '1' for the write operation.
2. Set the desired time or date register by writing to the appropriate counter register (RTC Registers 03h
to 0Fh).
3. Poll the CF bit in Control Register A. If the CF bit is '0', the write operation was successful and the
time or date register has been set.
4. If the CF bit is '1', a carry has occurred and the procedure must be repeated. The internal carry period
lasts for a maximum of 125 µs. Wait 125 µs before attempting the procedure again. Restart the
procedure by clearing the CF bit to '0' (Step 1).