[Gllug] Re: Dual core AMDs

[John Winters]

On Wed, 2005-07-13 at 15:55 +0100, Adrian McMenamin wrote:
> > Rich Walker wrote:
> > > Richard Huxton <dev at archonet.com> writes:
> > > 
> > > 
> > >>Richard Jones wrote:
> > >>
> > >>>Regarding Z80 "vs" 6502, I can't imagine anyone would actually want
> > >>>to program a 6502 after using a Z80 ...
> > >>
> > >>Then you've clearly been out in the sun too long sir.
> > >>
> > >>The 6502 represents the pinnacle of CPU design, before this current slide into transistor-mad
> > >>decadence ;-)
> > >>
> > >>Three registers are enough for anyone.
> > > 
> > > 
> > > You mean "256 registers, one accumulator, two index offset registers, and
> > > the ability to use any adjacent pair of registers for indirect
> > > addressing" is enough for anyone, shurely?
> 
> Now, correct me if I am wrong but these "256 registers" - what you
> really mean is the first 256 bytes of RAM? Sounds like a bit of
> sophistry to me

Not really.  The first 256 bytes of memory really did behave like
registers.

>  - and, anyway, does not compare to the Z80s memory
> transfer built ins - write your screen RAM in memory and - zap - load it
> up when the *cough* monitor - oh alright then, B&W portable TV - is in
> refresh

The LDIR on the Z80 always seemed a bit messed up to me.  It didn't
actually do it anything like as quickly as it could have done because it
went back and re-read the instruction again on every cycle.

	Program:	You see these bytes here (HL)
	CPU:		Yup!
	Program:	And you see that space there (DE)
	CPU:		Yup!
	Program:	Well take this many of the bytes (BC)
	CPU:		Yup!
	Program:	And copy them (LDIR)
	CPU:		(Copies 1 byte) What was it you wanted
			me to do again?
	Program:	Copy them! (LDIR)
	CPU:		(Copies 1 more byte)  Sorry, what was
			it again?
	Program:	Copy them!! (LDIR)
	...repeat ad nauseam

A bit like the CPU equivalent of ADD.

John

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