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X-Hacker.org- Interrupts & Ports - Norton Guide
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Port 043 - 8253-5 Mode Control
Only mode 2 and 3 used.
11xx xxxx 00=channel 0
01=channel 1
10=channel 2
xx11 xxxx 00=latch present value
01=read/write only MSB
10=read/write only LSB
11=read/write LSB, the MSB
xxxx 111x 000=mode 0: countdown with optional inhibit
(level output)
001=mode 1: countdown with optional restart
(level output)
010=mode 2: generate one pulse out of N
(used for DMA memory refresh
by channel 1)
011=mode 3: generate square wave
(used for channels 0 and 2)
100=mode 0: countdown with optional inhibit
(pulse output)
101=mode 1: countdown with optional restart
(pulse output)
xxxx xxx1 0=binary, 1=BCD counter decrementing
binary counting always used in PC
See Also: 8253-5 040 041 042 8237A-5 000 001
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