Ba + 9: 8254 Timer/Countor I - Real Time Devices AD1200 User Manual

Sets PCO to 1:
(written to BA +7)
For example, if you want to set Port C bit 0 to l, you would set up the control word so that bit 7 is 0; bits l, 2,
and 3 are 0 (this selects PC0); and bit 0 is 1 (this sets PCO to l). The conrrol word is set up like rhis:
D7 D6 D5 D4
D3 D2
D1 DO
X = don't care
Blr
Set PCO
Bit Select
000 = PCO
BA + 8: 8254 Timer/Counter 0 (ReadAVrite)
A read shows the count in the counter, and a write loads the counter witl a new value. Counting begins as soon
as the count is loaded. This counter is cascaded with TCI to form the 32-bit on-board pacer clock.
BA + 9: 8254 Timer/Counter 1(ReadMrite)
A read shows the count in the counter, and a write loads the counter with a new value. Counting begins as soon
as the count is loaded. This counter is cascaded with TCO to form fte 32-bit on-board pacer clock.
BA + 10: 8254 Timer/Counter 2 (Read/Write)
A read shows the count in the counter, and a write loads the counter with a new value. Counting begins as soon
as the count is loaded. This counter can be cascaded to TCO and TCI or it can be used independently.
BA + 11: 8254 Control Word (Write Only)
Accesses the 8254 control register to directly control the three timer/counters.
SeUReset
Functlon
Counter Selec
00 = Counter 0
01 = Counter 1
10 = Counter 2
11 = read back setting
Read/Load
00 = latching operalion
01 = read/load LSB only
10 = read/load MSB only
11 = read/load LSB, then MSB
D7 D6 D5 D4 D3
D2 D1 DO
Select
0
Counter
BCD/Binary
0 = binary
1 = B C D
Counter Mode Select
000 = Mode 0, evenl count
001 = Mode 1, programmable 1-shot
010 = Mode 2, rate generator
01 1 = Mode 3, square wave rate generator
100 = Mode 4, software-lriggered
strobe
101 = Mode 5, hardware-triggered
strobe
4-7