3 ms·

Here's the datasheet for the chip. https://archive.org/details/SPC81A/mode/1up https://archive.org/details/SPC81A/mode/1up A very simple SoC with what appears

Here's the datasheet for the chip. https://archive.org/details/SPC81A/mode/1up https://archive.org/details/SPC81A/mode/1up A very simple SoC with what appears to be a 6502 clone suspiciously missing anything to do with the Y register. Stack is also in a non standard place (the top half of the zero page), probably due to only having those 128 bytes of RAM total and not wanting to give up zero page access.

sircastor 4y ago
I read your comment out of context (actually in the context of programming an NES) and tried to figure out how the heck you’d live without a Y register. I’m not saying it’s not possible, but if I were writing a game It’d be a pain. Obviously it doesn’t Apply here.
djmips 4y ago
"The SPC81A 8-bit microprocessor is a high performance processor equipped with Accumulator, Program Counter, X Register, Stack pointer and Processor Status Register (this is the same as the 6502 instruction structure)." Well not exactly haha. Yeah, if you look at the source code. No Y register related instructions! I thought about it and you could get used to writing code without the Y register pretty quickly... The actual instruction set manual for SunPlus 6502 CPUs (covers several but you can see the low end doesn't have Y instructions) https://www.manualslib.com/products/Sunplus-Cpu6502-8692958.html https://www.manualslib.com/products/Sunplus-Cpu6502-8692958....