82C54 Datasheet, PDF (10/18 Pages) Intel Corporation – CHMOS PROGRAMMABLE INTERVAL TIMER

82C54
If an initial count is written while GATE ^e 0 it will
still be loaded on the next CLK pulse When GATE
goes high OUT will go high N CLK pulses later no
CLK pulse is needed to load the Counter as this has
already been done
MODE 1 HARDWARE RETRIGGERABLE
ONE-SHOT
OUT will be initially high OUT will go low on the CLK
pulse following a trigger to begin the one-shot pulse
and will remain low until the Counter reaches zero
OUT will then go high and remain high until the CLK
pulse after the next trigger
After writing the Control Word and initial count the
Counter is armed A trigger results in loading the
Counter and setting OUT low on the next CLK pulse
thus starting the one-shot pulse An initial count of N
will result in a one-shot pulse N CLK cycles in dura-
tion The one-shot is retriggerable hence OUT will
remain low for N CLK pulses after any trigger The
one-shot pulse can be repeated without rewriting the
same count into the counter GATE has no effect on
OUT
If a new count is written to the Counter during a one-
shot pulse the current one-shot is not affected un-
less the Counter is retriggered In that case the
Counter is loaded with the new count and the one-
shot pulse continues until the new count expires
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NOTE
The Following Conventions Apply To All Mode Timing
Diagrams
1 Counters are programmed for binary (not BCD)
counting and for Reading Writing least significant byte
(LSB) only
2 The counter is always selected (CS always low)
3 CW stands for ‘‘Control Word’’ CW e 10 means a
control word of 10 hex is written to the counter
4 LSB stands for ‘‘Least Significant Byte’’ of count
5 Numbers below diagrams are count values
The lower number is the least significant byte
The upper number is the most significant byte Since
the counter is programmed to Read Write LSB only
the most significant byte cannot be read
N stands for an undefined count
Vertical lines show transitions between count values
Figure 15 Mode 0
10
Figure 16 Mode 1
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