Electrical Engineering Stack Exchange
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Questions tagged [instruction-set]

Instruction set refers to the Assembly syntax based on a processor's architecture that interacts with its registers within the processing unit itself. There is a large variety of instruction sets including: MIPS, ARM, 68HC11/12, x86, and so forth.

The instruction set, also called instruction set architecture (ISA), is part of a computer that pertains to programming, which is basically machine language. The instruction set provides commands to the processor, to tell it what it needs to do. The instruction set consists of addressing modes, instructions, native data types, registers, memory architecture, interrupt, and exception handling, and external I/O.

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ISA opcodes---Where do they come from?

When engineers are designing an instruction set architecture, by what procedure or protocol, if any, do they follow when designating certain binary codes as instructions. For example, if I have an ISA that says 10110 is a load instruction, where did…
Steven
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How does an operating system or program detect the CPU model name?

What kind of binary compatibility is present for 2 processors sharing an Instruction Set?. I had asked a question on Computer Science Stack Exchange, to which I got an answer which said: As a trivial problem, you can write a program that will try…
Shashank V M
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Why do computers have only a few thousand instructions when they could have millions?

Most computers contain only a couple thousand instructions, but the bit width(usually 64-bit) technically allows computers to have access to millions or even billions of instructions. Some could be extremely useful, like DIVIDE, EXPONENT or…
Trevor Mershon
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How does an ARM processor in thumb state execute 32-bit values?

What I understand is, the ARM mode can execute 32-bit of instructions and Thumb mode can execute 16-bit of instructions. For instance, Here is the ARM instructions set: And Thumb instructions set: From these both instruction set tables, please…
user105009
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How can I do immediate addition in the Atmel AVR instruction set?

I've been doing some AVR assembly programming for a university course, and I recently happened upon a situation where I would have wanted an "add immediate" instruction. However, no such instruction seems to exist within the Atmel AVR instruction…
Newbyte
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Are `call` and `return` usually instructions in a modern ISA?

I've been working through the problems in a game based around building a Turing Complete machine. One of the final problems asks you to implement the call and return instructions. This makes it seem like they're part of the ISA and need to be…
Connor
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Are processor instruction sets royalty free? (e.g. ARM v9, x86)

I asked a general question on Law SE with one example (ARM) and for that example, I was directed to What exactly does ARM sell to vendors?. I've read that QA that ARM sells actual core designs. I've read about RISC-V and ARM on Wikipedia and some…
Martian2020
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What is the role of ISA (Instruction Set Architecture) in the comp arch abstraction stack.

I have programming background, and I recently started taking computer architecture course. Most of the lectures I see use the some sort of the layering as described in the following diagram explaining what will be covered in the course. The…
Vivek Maran
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What happens when you fall off the end of main() in a PIC?

Another question included this program: void main(void){ TRISD = 0x00; PORTD = 0xFF; } Let us assume that it does exactly what was intended up through the last line of main(). My question is, what happens in a PIC18F4550 when the flow of…
Warren Young
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How do you fit so many instructions on a 8-bit processor?

I will preface this that it is highly likely that I have misunderstood how Harvard architecture works, but I cannot understand how an 8-bit instruction set, say the ATmega128 for example, can contain 133 instructions along with the addresses to 32*8…
Lyndon Alcock
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Designing an instruction set for a homebrew computer

I'm going to begin the adventure of building an 8-bit homebrew computer. Right now, I'm considering the instruction set. SAP-1 seems a bit too sparse, so I'm designing my own. Some facts: My primary goal is to learn. I'll be building this on…
Peter
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8085 ;JMP instruction

How exactly is JMP XXXXH; executed ? First the PC(Program counter) will contain the address where this instruction is present. In first machine cycle opcode will be fetched and PC will be incremented . Now in the second machine cycle we have to…
Urooj
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How can a 4-bit CPU have 40 instructions?

Currently, I am using Logisim (yes, still Logisim) to build a 4-bit variant of the 8-bit SAP-1 microcomputer. However, I ran into a problem with the instruction register. Let me explain. The SAP-1 has 5 instructions (LDA, ADD, SUB, OUT, HLT). These…
Trevor Mershon
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8085 ; High impedance state of lower order address/multiplexed data bus during memory read and write machine cycles

The two pictures are of memory read and write machine cycles . Could somebody please explain why in memory read cycle the lower order address / multiplexed data bus is in high impedance state at the positions I've marked with red in the timing…
Urooj
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ARM Instruction size vs Instruction encoding

I cannot make sense of the difference between 'Instruction size' and 'Instruction encoding' specially about ARM and Thumb ISA's as explained here: Can we say that Instruction size is 32 bits but its encoding is 16-bits for Thumb-1 ISA and 32 bits…
alt-rose
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