Intel 386 - Manual (Page 256)

10-13
TIMER/COUNTER UNIT
Figure 10-11. Mode 3 – Basic Operation (Even Count)
Odd count basic operation:
1. After a control word write, OUTn is driven high.
2. On the CLKINn pulse following a gate-trigger or when the count rolls over, count minus
one is loaded.
3. On each succeeding CLKINn pulse, the count is decremented by two.
4. When the count rolls over, OUTn is driven low and the count minus one is loaded. (This
causes OUTn to stay high for one more CLKINn pulse than it stays low.)
5. On each succeeding CLKINn pulse, the count is decremented by two.
6. After the count reaches terminal count, OUTn is driven high and the count minus one is
loaded.
7. The process is repeated from step 3.
? ? ? ? 0004 0002 0004 0002 0004 0002 0004 0002
Writes to
Counter n
CLKIN n
GATE n
OUT n
Control
Word = 16H
Count 0004 0002
Count = 4
A2314-01