Ziatech Corporation ZT 8809A, Руководство по эксплуатации

Страница: 253 / 412

Counter/Timers (8254)
This allows the sequence to be "retriggered" by software. OUT
strobes low N + 1 CLK pulses after the new count of N is written.
Mode 5: Hardware Triggered Strobe
OUT is initially high. Counting is triggered by a rising edge of
GATE. When the initial count has expired, OUT goes low for one
CLK pulse and then goes high again.
After writing the Control Word and initial count, the counter is not
loaded until the CLK pulse after a trigger. This CLK pulse does not
decrement the count. So for an initial count of N, OUT does not
strobe low until N + 1 CLK pulses after a trigger.
A trigger results in the counter being loaded with the initial count on
the next CLK pulse. The counting sequence is retriggerable. OUT
does not strobe low for N + 1 CLK pulses after any trigger. GATE has
no effect on OUT.
If a new count is written during counting, the current counting
sequence is not affected. If a trigger occurs after the new count is
written but before the current count expires, the counter is loaded with
the new count on the next CLK pulse and counting continues from
there.
11-21