Reverse engineering old chips Ken Shirriff
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Instruction decoding<br />
PLA<br />
Instruction<br />
register<br />
Control lines<br />
Data bus<br />
Decode instruction, generate control signals.<br />
PLA: regular array of gates, very common in 1970s.<br />
Now microcode.<br />
Instruction stored in instruction register.<br />
Each PLA column selects a bit pattern from<br />
instructions.<br />
Design instruction set correctly.
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