Operate Instruction

Instruction format 7XXX: XXX Bits control internal logic. Not all combinations do useful things.

• AC: IAC – Increment CLA – Clear CMA – Complement
• RAL, RTL – Rotate 1,2 left RAR, RTR – Rotate 1,2 right
• OSR – Or switch register with AC.
• Link: CLL – Clear CML – Complement.
• Skip: SKP – Skip SNL – Skip non zero link, SZA – Skip zero AC
• SMA – Skip minus AC Inverse skips also.
• HLT – Halt.
• These are group 1 and 2. Order of multiple operations is specified. Some variation between PDP-8 models.
• Group 3 is EAE which if installed gives 12x12 to 24 multiply, 24/12 divide with 12 bit result and 12 bit remainder, shift, normalize, add etc. MQ register used for second 12 bits, third from location following instruction.