From: Erik Slagter <erik_at_slagter.name>
Date: Sat, 18 Aug 2007 17:15:24 +0200

Bluechip wrote:
> At 10:47 18/08/2007, you wrote:
>> Vladimir Pantelic wrote:
>>
>> > The data sheet says 8bit! There is a DSP that does the MP3 decoding and
>> > a DMA controller, so most likely the z80 does little besides reading
>> the
>> > FAT filesystem and setting up the DMA to pipe data from Flash to the
>> DSP.
>>
>> Actually the Z80 is an 8-bit CPU with some 16-bit extensions. For
>> example it can combine six 8-bit registers into three 16-bit registers,
>> and do some simple arithmetic on them (add/sub). This may not sound
>> impressive, but it is way easier to program than a pure 8-bit CPU like
>> the 6502/6510 which doesn't know of 16-bit at all.
>
> There are registers other than BC DE and HL which behave as 16bit
> "register-pairs", not least of all the index registers IX and IY, there
> are also shadow registers and 16bit memory accessing instructions to
> consider above and beyond a 'pure' 8bit machine.

EXX ;-)

But I wouldn't call these shadow registers very useful, as you can only
exchange them all at once with the other set of registers. And of course
there are the index registers, but they require rediculous lengthy
opcodes especially in combination with the CBh and EDh opcode "modifiers".

BTW offtopic: I would have been very happy if the 68000-series had
become the industry-standard instead of i386, it has one of the neatest
sets of opcodes I have ever seen (and used), it's almost like you're
programming in C.

Received on 2007-08-18