[A83] Re: IXIY
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[A83] Re: IXIY
Can I ld stright to IX and IY, or do I need to push hl/pop ix?
At 02:57 PM 9/15/2001 +0200, you wrote:
>IX and IY can be used as equivalents for HL. You can use them as any other
>16 bit register, though they're slower. In fact they also exist out of two 8
>bit registers (IXH, IXL, IYH, IYL), but these are undocumented. What makes
>IX and IY special is in there name, index registers.
>
>Let's say you have a block of data somewhere and that you frequently need to
>access parts of it. Then you can consider using IX or IY. You set one of
>those to the start of that block and when you then need byte number 5, you
>just LD (IX+05h). If you would use HL for that matter you first need to add
>5 before you can read the contents of the byte at that location.
>
>The TIOS uses IY. It sets that register to the start of the ram area where
>all the flags are stored. It is then very simple to set,reset bits or to
>load values from that area.
>
>ionPutSprite uses IX as a normal 16 bit register. Even though this is slower
>than using HL, it is better to use IX, because HL is already used, so you'd
>have to push/pop and that is slower.
>
>
> >From: Gavin Olson <gtolson@snet.net>
> >
> >In several recent messages, there has been talk of the index registers
> >IX and IY. I know that ionputsprite uses IX as the address, and the
> >set and res statements for changing flags use the IY register as a
> >base address, but I have no idea as to what makes these registers
> >special, as in why ionputsprite doesn't use hl, and as to how the
> >value in IY is always predictable, in that it can be used as a base
> >address for those flags, even though many people have code that
> >modifies it.
> >
> >-Gavin Olson
> >
> >
> >
> >
>
>
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