Register Assignments

The 6000 series has three banks of registers. The data registers (X0-X7) hold 60-bit arguments and results from the machines more complex computations such a long integer and floating point arithmetic. All memory references go through these registers. The 18-bit index registers are used for address calculation or other counting. The 18-bit address registers (mostly) retain the machine addresses of recent memory operations. Setting some address registers (A1-A5) initiate a memory read to the corresponding X register. Setting other address registers (A6-A7) initiate a memory write from their corresponding X registers. A0 (and X0) are free of this side effect.

PDP-8 Simulator
© 1975, 1998, Ward Cunningham
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