ADLINK PCI-7300A - Manual (Page 79)

Appendix A 8254 Programmable Interval Timer
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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.