8254
231164–8
Figure 16. Mode 1
initial count has expired, OUT goes low for the re-
mainder of the count. Mode 3 is periodic; the se-
quence above is repeated indefinitely. An initial
count of N results in a square wave with a period of
N CLK cycles.
GATE
e
1 enables counting; GATE
e
0 disables
counting. If GATE goes low while OUT is low, OUT is
set high immediately; no CLK pulse is required. A
trigger reloads the Counter with the initial count on
the next CLK pulse. Thus the GATE input can be
used to synchronize the Counter.
After writing a Control Word and initial count, the
Counter will be loaded on the next CLK pulse. This
allows the Counter to be synchronized by software
also.
Writing a new count while counting does not affect
the current counting sequence. If a trigger is re-
ceived after writing a new count but before the end
of the current half-cycle of the square wave, the
Counter will be loaded with the new count on the
next CLK pulse and counting will continue from the
12
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