Intel 8253 - Max Count

4-12
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 2
16
for binary counting and 10
4
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.
FIGURE 15. GATE PIN OPERATIONS SUMMARY
FIGURE 16. MINIMUM AND MAXIMUM INITIAL COUNTS
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
counting
2) Sets output im-
mediately high
Initiates Counting Enables Counting
3 1) Disables
counting
2) Sets output im-
mediately high
Initiates Counting Enables Counting
4 1) Disables
Counting
- Enables Counting
5 - Initiates Counting -
MODE MIN COUNT MAX COUNT
010
110
220
320
410
510
NOTE: 0 is equivalent to 2
16
for binary counting and 10
4
for BCD
counting.
82C54