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4.4) My Real Time Clock has paused, how do I restart it?




Description

This article is from the comp.sys.acorn FAQ, by Paul Vigay with numerous contributions by others.

4.4) My Real Time Clock has paused, how do I restart it?

This is a problem caused most often by 'rogue' software chatting to the IIC bus and incorrectly setting the pause bit on the RTC control register. Symptoms of this happening are that the time is always the same every time you reboot and the software clock tends to run slightly slow (losing about a minute every hour or so.). If you are experiencing these symptoms this program should restart your RTC clock :-

REM poke RTC control register
REM  Bit   0         1
REM   7   Count  ResetDivider
REM   6   Count  HoldLastCount
REM write 0 for normal operation, write &80 or &40 freezes RTC
DIM cmosdata% 16
!cmosdata%=&00000000
REM write 0 twice to RTC, first 0 is address- control reg
REM second is control reg value 0 is default i.e. clock on
SYS &240, &A0, cmosdata%,2
END

You will need to reset the time after running this program but hopefully your RTC will keep the correct time from here on in.

If the same symptoms persist after trying this program contact your local Acorn dealer as something more serious has gone wrong. Note that to check that the symptoms are persisting you must reboot your machine after running this program and having set the time. This is due to the way RISC OS maintains a 'soft' copy of the real time clock and until you reboot it will not be obvious whether your RTC has indeed started working again.

 

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