[A83] Re: IXIY
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[A83] Re: IXIY
You can do ld ix,NNNN and ld ix,(NNNN).
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Original Message
From: "Gavin Olson"<gtolson@snet.net>
Subject: [A83] Re: IXIY
Date: Sat, 15 Sep 2001 14:47:17 -0400
>
>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
>> >
>> >
>> >
>> >
>>
>>
>>_________________________________________________________________
>>Download MSN Explorer gratis van http://explorer.msn.nl/intl.asp
>
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