82C54 Datasheet, PDF (12/17 Pages) Intel Corporation – CHMOS PROGRAMMABLE INTERVAL TIMER

82C54
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 count-
ing, and continues counting. Modes 2 and 3 are periodic; the
Counter reloads itself with the initial count and continues
counting from there.
SIGNAL
STATUS
MODES
LOW OR
GOING LOW
RISING
HIGH
0 Disables Counting
-
Enables Counting
1
-
1) Initiates
-
Counting
2) Resets output
after next clock
2 1) Disables
Initiates Counting Enables Counting
counting
2) Sets output im-
mediately high
3 1) Disables
Initiates Counting Enables Counting
counting
2) Sets output im-
mediately high
4 1) Disables
Counting
-
Enables Counting
5
-
Initiates Counting
-
MODE
MIN COUNT
MAX COUNT
0
1
0
1
1
0
2
2
0
3
2
0
4
1
0
5
1
0
NOTE: 0 is equivalent to 2¹⁶ for binary counting and 10⁴ for BCD
counting.
FIGURE 16. MINIMUM AND MAXIMUM INITIAL COUNTS
FIGURE 15. GATE PIN OPERATIONS SUMMARY
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