jfd instruction

[Bill E]

I might have asked this before, can't remember. But, I have some details. I see this listed in the common 'PDP 1 Instruction List' card as opcode 12. However, I haven't seen it documented anywhere else, pidp-1 doesn't implement it and simh doesn't either.

From the little info I found, the one brief description says it's for use with the sequence break system when in extended memory mode, possibly otherwise, and it appears to 

do a full restore of the data saved in the interrupt locations, the IO and AC and PC in one operation.

Anyone have any clues? It seems like it might be useful if it actually exists.

Bill

[Bill E]

Sorry, I did ask a while back and got a good answer. Losing my mind, apparently. Too much coding?

Bill

[Glenn Babecki]

BTW, what was the answer to your question(s)?

On Fri, Jan 2, 2026, 4:03 PM Bill E <wjegr...@gmail.com> wrote:

Sorry, I did ask a while back and got a good answer. Losing my mind, apparently. Too much coding?

Bill

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[Bill E]

See https://groups.google.com/g/pidp-1/c/pZl2zyVhi2g/m/Ab6TjCoiBQAJ

On further research, I think it's meant to work with the type 151 core memory system, of which I can find no decent documentation. However, it seemed to support separate banks for data and instructions, not sure.

Bill