CS82C54 datasheet(12/22 Pages) INTERSIL

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82C54

If an initial count is written while GATE = 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.

NOTES: 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 = 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.

6. N stands for an undefined count.

7. Vertical lines show transitions between count values.

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 N CLK cycles in duration. 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 unless the

Counter is retriggerable. In that case, the Counter is loaded

with the new count and the one-shot pulse continues until

the new count expires.

CW = 10

LSB = 4

CLK

GATE

OUT

CLK

GATE

OUT

CLK

GATE

OUT

CW = 10

LSB = 3

CW = 10

LSB = 3

LSB = 2

NNN

NNNN

FIGURE 9. MODE 0

CLK

GATE

OUT

CLK

GATE

OUT

CLK

GATE

OUT

CW = 12

LSB = 3

CW = 12

LSB = 3

CW = 12

LSB = 2

LSB = 4

NNN

NNNN

FIGURE 10. MODE 1

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