Re: Aw: [stella] X or Y ?

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
Unsub & more at

Current Thread