Subject: Re: Aw: [stella] X or Y ? From: "Eric Ball" <ericball@xxxxxxxxxxxx> Date: Thu, 15 Apr 2004 16:23:32 -0400 |
> > There's no "absolute zeropage" adressing mode to some instructions using Y, so the code rendered in those cases will force an absolute 16-Bit adressing padded with "00" for the HI-Byte and so wasting an extra byte. > > Actually, the _only_ instructions that can do an 8-bit zeropage address > with a Y index, are LDX and STX. Everything else always uses a 16-bit > address if indexing with Y (DASM will silently do that for you.) It takes the same 4 cycles in either mode, so it doesn't matter except > for the one extra byte of ROM. Well, to be completely pathological (and nit-picky) ABS,X/Y will go over a page boundary (+1 cycle), while ZP,X/Y will not. So with ZP,X/Y you can have a negative index. Why? I don't know, but it's there none the less. ---------------------------------------------------------------------------------------------- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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