9 ms·
Oh please, the big improvement in the Z80 over the 8080 was the IX and IY instructions plus the alternate register set 'AF etc and that's completely absent in t
by djmips 4y ago
Oh please, the big improvement in the Z80 over the 8080 was the IX and IY instructions plus the alternate register set 'AF etc and that's completely absent in the Gameboy CPU. The Z80 is not the father of the Gameboy CPU. A+B-B = A
The Z80 has some influence but it's pretty small.
- flohofwoe 4y agoI wouldn't call the IX/IY instructions an improvement. They were so slow that they've rarely been used in performance-sensitive code (like games), it totally makes sense to drop them in a gaming device. Same for the block instructions in the ED instruction range, quite convenient, but also very slow. LDI/LDD might have been useful for blitting bytes in unrolled loops, but since (AFAIK) the GB video hardware renders tiles and sprites directly, there's hardly a need for copying lots of bytes around. The shadow register set wasn't all that useful either except for quickly saving state in interrupt handlers, but the additional registers take up a lot of die space. On the other hand, the entire block of 256 bit twiddling instructions were obviously deemed important enough to keep them in the Gameboy CPU.
- djmips 4y agoSo you're basically saying you use a Z80 like an 8080. That's fine.:) But I will admit that the CB array of instructions are quite useful and Z80 in origin. But just because you don't like a bunch of the Z80 die doesn't mean that the SM83 is a Z80 though. It's basically just an 8080 + CB and instructions that appear neither in 8080 or Z80 Still - I can see both from both sides now.