ADLINK PCI-7300A User Manual
Page 79
Appendix A 8254 Programmable Interval Timer
• 71
Before loading or reading any of these individual counters, the control byte
(Base + C) must be loaded first. The format of control byte is:
Control Byte: (Base + 7, Base + 11)
Bit
7
6
5
4
3
2
1
0
SC1
SC0
RL1
RL0
M2
M1
M0
BCD
•
SC1 & SC1 - Select Counter (Bit7 & Bit 6)
SC1
SC0
COUNTER
0
0
0
0
1
1
1
0
2
1
1
ILLEGAL
•
RL1 & RL0 - Select Read/Load operation (Bit 5 & Bit 4)
RL1
RL0
OPERATION
0
0
COUNTER LATCH
0
1
READ/LOAD LSB
1
0
READ/LOAD MSB
1
1
READ/LOAD LSB FIRST, THEN MSB
•
M2, M1 & M0 - Select Operating Mode (Bit 3, Bit 2, & Bit 1)
M2
M1
M0
MODE
0
0
0
0
0
0
1
1
x
1
0
2
x
1
1
3
1
0
0
4
1
0
1
5
•
BCD - Select Binary/BCD Counting (Bit 0)
0
BINARY COUNTER 16-BITS
1
BINARY CODED DECIMAL (BCD) COUNTER (4
DECADES)
Note:
1. The count of the binary counter is from 0 up to 65,535.
2. The count of the BCD counter is from 0 up to 99,999.