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the timer update controls takes place.
Instead of multiplying the counter value
by 5 to get the correct number to sub-
tract from the timer, the 50 cycle
machine timer interrupt routine multi-
ples the counter value by 6.
This is
necessary because on a 50 cycle machine,
the counter is full every .3 seconds
instead of every .25 seconds.
We still
want the value 300 to be subtracted from
the timer each second.
By using a mul-
tiplier of 6 for 50 cycle machines, and
a multiplier of 5 for 60 cycle machines,
the same value
(30~
is subtracted from
the timer on all machines.
This allows
timer programming to be compatible for
all machines.
5-51
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