Ziatech Corporation ZT 8809A, Руководство по эксплуатации

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Counter/Timers (8254)
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 counting) and continues
counting. Modes 2 and 3 are periodic. The counter reloads itself with
the initial count and continues counting from there.
Table 11-3
Minimum and Maximum Initial Counts.
Mode
Minimum Maximum
Count Count
0 1 0
1 1 0
2 2 0
3 2 0
4 1 0
5 1 0
Note: 0 is equivalent to 2
16
for binary counting and 10
4
for BCD
counting.
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