Questions tagged [instruction-set]

For questions regarding the instruction sets of microprocessors.

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8
votes
1answer
409 views

Was there ever a division instruction with sign of the remainder following the sign of the quotient?

A document about the precursor to ANDF (Architecture Neutral Distribution Format) mentions that two of its integer division/remainder primitives "are those generally implemented directly by processor ...
10
votes
1answer
553 views

Timing and microcode in the PDP-11/40

I've been trying to figure out how the sequence of microcode instructions as described in the [schematics and ROM listing][1] in the PDP-11/40 (KD11-A Processor) relates to the timings given in ...
11
votes
3answers
878 views

Was the PDP-11 coroutine instruction actually used?

In a typical description of the coroutine mechanism it usually mentioned that the PDP-11 instruction set provided a way to effect the coroutine switch by a single instruction, namely JSR PC,@(SP)+. ...
46
votes
2answers
7k views

Why did the PDP-11 include a JMP instruction?

The PDP-11's program counter was addressable in two ways: as a general purpose register or as a memory location. Still, the PDP-11's instruction set included separate instructions for moving a new ...
13
votes
2answers
2k views

What is the instruction set of the PDP-7?

The PDP-7 was a bookshelf-sized "minicomputer", with keyboard, magnetic and paper tape and printer I/O. According to Wikipedia, the first version of UNIX (then named Unics) was programmed in assembly ...
44
votes
2answers
11k views

How did the Z80 instruction set differ from the 8080?

The Zilog Z80 microprocessor, known for its use in the ZX Spectrum, was designed to be a backwards-compatible extension to the Intel 8080 processor. It introduced several new instructions to the 8080'...
57
votes
3answers
6k views

How does the LOADALL instruction on the 80286 work?

This undocumented instruction existed in the 80286 and, I believe, the 80386. I think it was added while debugging the chip, so the engineers could quickly put the processor into any state and test it ...

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