Warp wrote:
> Darren New <dne### [at] sanrrcom> wrote:
>>>   Just because the 16-bit operations are performed on pairs of 8-bit
>>> registers that doesn't make it any less of a 16-bit operation.
> 
>> OK. I guess we're just disagreeing about whether that ability makes a 
>> CPU an "8-bit CPU" or a "16-bit CPU".
> 
>   IMO "16-bit CPU" means "can perform most calculations on 16-bit values
> with single opcodes". 

I'm pretty sure the 8080 at least was not like that.

Hmmm... A quick google shows opcodes like "add hl,bc" and such, as well 
as some subtracts, but many more opcodes for 8-bit than 16-bit ops. (And 
some extra prefix codes for IX and IY, yes.) The accumulator, for 
example, was 8 bits, and (IIRC) you couldn't load a 2-byte address into 
a two-byte pointer register unless it was an absolute address.

The 8080 had no such opcodes at all, from what I can see (and what I 
remember). I probably stopped programming in assembler before the Z80 
was widespread enough you could just rely on it being there instead of 
an 8080. :-)

>   Could you calculate eg. additions and substractions using 16-bit values
> with single opcodes?

Nope.

OK, so you're saying a 16-bit CPU has a 16-bit ALU? I'm not sure how 
wide the Z80's ALU was. I wouldn't be surprised if "sub bc,hl" was 
calculated with two runs thru the ALU.

Anyway, as I said, I think at this point we're just discussing what one 
wants to call the CPU, without adding any additional information to it.

-- 
Darren New / San Diego, CA, USA (PST)
  Helpful housekeeping hints:
   Check your feather pillows for holes
    before putting them in the washing machine.

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