Control Byte
Before loading or reading any of these individual counters, the control byte (BASE+3) must be loaded first. The format of the control byte is :
0
i t
B
C
D
∙SC1 & SC0 - Select Counter (Bit7 & Bit 6)
S | S | COUNTER |
C | C |
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1 | 0 |
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0 | 0 | Select Counter 0 |
0 | 1 | Select Counter 1 |
1 | 0 | Select Counter 2 |
1 | 1 | ILLEGAL |
∙RL1 & RL0 - Select Read/Load operation (Bit 5 & Bit 4)
R | R | OPERATION |
L | L |
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1 | 0 |
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0 | 0 | COUNTER LATCH FOR STABLE READ |
01 READ/LOAD LSB ONLY
10 READ/LOAD MSB ONLY
11 READ/LOAD LSB FIRST, THEN MSB
∙M2, M1 & M0 - Select Operating Mode (Bit 3, Bit 2, & Bit 1)
M2 | M1 | M0 | MODE |
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0 | 0 | 0 | 0 |
0 | 0 | 1 | 1 |
x | 1 | 0 | 2 |
x | 1 | 1 | 3 |
1 | 0 | 0 | 4 |
1 | 0 | 1 | 5 |
