ID82C54【PDF 7/22 页】IC OSC PROG TIMER 8MHZ 24DIP

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Counter will be loaded with new count on the next CLK pulse

and counting will continue from there.

Operation Common To All Modes

Programming

When a Control Word is written to a Counter, all Control

Logic, is immediately reset and OUT goes to a known initial

state; no CLK pulses are required for this.

Gate

The GATE input is always sampled on the rising edge of

CLK. In Modes 0, 2, 3 and 4 the GATE input is level

sensitive, and logic level is sampled on the rising edge of

CLK. In modes 1, 2, 3 and 5 the GATE input is rising-edge

sensitive. In these Modes, a rising edge of Gate (trigger)

sets an edge-sensitive flip-flop in the Counter. This flip-flop

is then sampled on the next rising edge of CLK. The flip-flop

is reset immediately after it is sampled. In this way, a trigger

will be detected no matter when it occurs - a high logic level

does not have to be maintained until the next rising edge of

CLK. Note that in Modes 2 and 3, the GATE input is both

edge-and level-sensitive.

Counter

New counts are loaded and Counters are decremented on

the falling edge of CLK.

The largest possible initial count is 0; this is equivalent to 216

for binary counting and 104 for BCD counting.

The counter does not stop when it reaches zero. In Modes 0,

1, 4, and 5 the Counter “wraps around” to the highest count,

either FFFF hex for binary counting or 9999 for BCD

counting, and continues counting. Modes 2 and 3 are

periodic; the Counter reloads itself with the initial count and

continues counting from there.

NNN

CLK

GATE

OUT

CW = 1A LSB = 3

NNN

CLK

GATE

OUT

CW = 1A LSB = 3

CLK

GATE

OUT

CW = 1A LSB = 3

LSB = 5

FIGURE 14. MODE 5

SIGNAL

STATUS

MODES

LOW OR

GOING LOW

RISING

HIGH

Disables Counting

Enables Counting

1) Initiates

Counting

2) Resets output

after next clock

1) Disables

counting

2) Sets output

immediately high

Initiates Counting Enables Counting

1) Disables

counting

2) Sets output

immediately high

Initiates Counting Enables Counting

1) Disables

Counting

Enables Counting

Initiates Counting

FIGURE 15. GATE PIN OPERATIONS SUMMARY

MODE

MIN COUNT

MAX COUNT

010

110

220

320

410

510

NOTE: 0 is equivalent to 216 for binary counting and 104 for BCD

counting.

FIGURE 16. MINIMUM AND MAXIMUM INITIAL COUNTS

82C54

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