Comment by sfink

Comment by sfink 2 days ago

What is this "LD A, 0" syntax? Is it a z80 thing?

One of the random things burned into my memory for 6502 assembly is that LDA is $A9. I never separated the instruction from the register; it's not like they were general purpose. But that might be because I learned programming from the 2 books that came with my C64, a BASIC manual and a machine code reference manual, and that's how they did it.

I learned assembly programming by reading through the list of supported instructions. That, and typing in games from Compute's Gazette and manually disassembling the DATA instructions to understand how they worked. Oh, and the zero-page reference.

Good times.

Narishma 2 days ago

> One of the random things burned into my memory for 6502 assembly is that LDA is $A9. I never separated the instruction from the register; it's not like they were general purpose.

You had LDA and LDX and LDY as separate instructions while the Z80 assembler had a single LD instruction with different operands. It's the same thing really.

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sfink 2 days ago

Right, though the LD? and ST? instructions were kind of exceptions. You could only do arithmetic and stack and bitwise ops (and, or, eor, shift, rotate) with A, never X nor Y. Increment and decrement were X/Y only. You couldn't even add two registers together without stashing one in memory.

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vanderZwan a day ago

> What is this "LD A, 0" syntax? Is it a z80 thing?

Well, I never wrote any 6502 so I can't compare, but yes, you could load immediate values into any register except the flag register on the Z80. Was that not a thing on the 6502?

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