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The data format for the control register appears below:
BASE+ 27 8254 co n t r o l, st an d ar d m o d e
Bit
D7
D6
D5
D4
Value
SC1
SC0
RW1
RW0
Description:
SC1 & SC0
Select counter
Counter
SC1
0
0
1
0
2
1
Read-back command
1
RW1 & RW0
Select read/write operation
Operation
RW1
Counter latch
0
Read/write LSB
0
Read/write MSB
1
Read/write LSB first,
1
then MSB
M2, M1 & M0
Select operating mode
M2
M1
M0
Mode
0
0
0
0 programmable one shot
0
0
1
1 programmable one shot
X
1
0
2 Rate generator
X
1
1
3 Square wave rate generator
1
0
0
4 Software triggered strobe
1
0
1
5 Hardware triggered strobe
Appendix A Function of 8254 counter Chip
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D3
D2
D1
D0
M2
M1
M0
BCD
SC0
0
1
0
1
RW0
0
1
0
1
25
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