History of Game Boy Advance/Talk

	Revision 7 . . December 5, 2001 5:51 am by Damian Yerrick [summarized old talk; 6502 emulation on GBA]
	Revision 6 . . (edit) October 4, 2001 4:35 pm by Drj [z80 and 6502 not same.]

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Difference (from prior major revision) (no other diffs)

Changed: 3c3

Someon changed separate z80 CPU to integrated 6502 CPU. Now, I think that it is a z80 CPU, same as on Game Boy, different to SNES (which was 6502!). I don't care to speculate as to whether the CPU is on the same die as the ARM or not, but if I had to guess then on the same die seems very plausible. Will try and find some evidence. --drj Definitely Z80.

Damian Yerrick summarized old talk:

Changed: 5,6c5,9

According to official programming manual, "integral 8 bit CISC CPU for compatibility". In context it seemed to say that the CPU was integrated, and the ARM in it *is* a custom chip for nintendo, but now it implies to me its integrated into the "system". I swear I read this somewhere else too, but for right now its too ambiguous so I'll take it out. (the block diagram doesn't show it as integrated either).

Game Boy products contain a "integral 8 bit CISC CPU for compatibility," namely the same Sharp Z80-like CPU (not an official Zilog design) used in the Game Boy Color. It runs at 4 MHz when playing GB titles and 8 MHz when playing GBC titles. GBA does not contain a 6502 processor (as somebody changed); Z80 instructions are completely incompatible with MOS Technologies 6502 instructions. Z80 and 6502 are not members of the same family; their instruction sets and timings aren't even close. We're not sure whether the ARM7TDMI and the GBZ80 are on the same die.

Removed: 8d10

BTW, I was thinking original GB when I said 6502, however, aren't they about the same pinout? technically the GBC CPU is a z80 "clone", of which 6502 and LR35902 are family members? I seem to recall certain variant instructions being unsupported in the GB because of this. (maybe this topic can flesh out the GBC entry.

Changed: 10c12,14

Game Boy and Game Boy Color use a Z80 clone. Few people care about it being a clone. Anyway most decent clones are in fact licensed designs from Zilog. 4MHz for the Game Boy, 8 MHz for the Game Boy Color (running at 4 MHz when playing grey Game Boy carts).

Just for reference, the 6502 processor (with BCD mode removed) was used in NES; the Super NES used a [WDC 65C816]?. However, the existence of the PocketNES? emulator for GBA proves that NES emulation (and thus 6502 emulation) on ARM is far from impossible. --Damian Yerrick

Changed: 12c16

The 6502 is a different beast altogether. It is an 8 bit CPU, but totally incompatible with the z80. --drj