All Questions
Tagged with instruction-set assembly
8
questions
11
votes
2
answers
645
views
IMPI Instruction set: is there any reference?
I've had an IBM 9404 B-10 for some time and I'm curious about its assembly language. I'm fully aware the AS lines were designed with portability in mind as much IBM didn't seem to provide assembly ...
14
votes
2
answers
2k
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Origin of "arithmetic" and "logical" for signed and unsigned shifts
The assembly language for many processors use the phrase "arithmetic shift" to represent the bitwise shift of a signed value, and "logical shift" for an unsigned value. The two ...
22
votes
1
answer
1k
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When did the IBM 650 have a "Table lookup on Equal" instruction?
In 1959, Donald Knuth wrote an assembly program named SuperSoap for the IBM 650. Here is the manual, and here is a listing of the program (in SuperSoap assembly language). Quoting from the abstract:
...
17
votes
5
answers
2k
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Has there ever been a instruction set architecture that did not require instruction decoding at all?
I am studying basic principles of instruction set architectures and am considering what it would take to not have any instruction decoding at all. I.e., all the control lines of the computer would be ...
88
votes
9
answers
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Why is the processor instruction called "move", not "copy"?
Many processors have an instruction called "move" (sometimes spelled MOV) which copies data from one location (the "source") to another (the "destination") in registers and/or memory. It does not do ...
24
votes
4
answers
4k
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Why are branches relative in many 8-bit CPUs?
I was looking over an old article on the 6809 and was perusing the opcodes and noticed that the branch instructions came in two flavors, long and short. That sparked a memory about one of the 6502-...
21
votes
8
answers
11k
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Uses for the halt instruction?
What was the halt instruction in early CPUs such as the Z80 and 8080 used for?
Here's a description of the Z80 instruction:
The HALT instruction suspends CPU operation until a interrupt or reset ...
48
votes
4
answers
8k
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Why are first four x86 General Purpose Registers named in such unintuitive order?
On x86 the first four general-purpose registers are named AX, CX, DX, BX. It would be quite intuitive if their indices (those used in instruction encoding) were in alphabetical order, but instead of ...