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8254

PROGRAMMABLE INTERVAL TIMER

Intel 

8254

MODE 5 HARDWARE TRIGGERED STROBE

(RETRIGGERABLE)

OUT will initially be high Counting is triggered by a

rising edge of GATE When the initial count has ex-

pired OUT will go low for one CLK pulse and then

go high again

After writing the Control Word and initial count the

counter will not be 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 a 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 will not strobe low

for N a 1 CLK pulses after any trigger GATE has

no effect on OUT

If a new count is written during counting the current

counting sequence will not be affected If a trigger

occurs after the new count is written but before the

current count expires the Counter will be loaded

with the new count on the next CLK pulse and

counting will continue from there

Figure 20 Mode 5

231164 – 12

16

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