Z80 vs 6502

[John Kennedy]

OK, I'm wanted definitive proof the Z80 (and by extension the 8080!) was better than the 6502, but currently there are a lot of people who are wrong. Feel free to cast your vote!

https://twitter.com/JohnKennedyMSFT/status/1380929670363840515?s=20

[Phillip L Harbison]

John Kennedy wrote:
> OK, I'm wanted definitive proof the Z80 (and by extension the 8080!) was
> better than the 6502, but currently there are a lot of people who are
> wrong. Feel free to cast your vote!

I've written tons of assembler code for both of them. I prefer the 6502
instruction set when writing assembler code, but it would not make a
very good host for C. I used Small C and QC on the Z80. While it is a
terrible host at least it worked. The 6809 beats both of them for C as
does the 68K.

The Z80 family did have some interesting peripherals like the SIO chip,
but the 6522 was the better parallel port. It is fairly easy to mix and
match using a "motel" circuit.

--
Phil Harbison

[Roger Linhart]

I did a lot more assembly language programming for the Z80 (work) vs 6502 (Commodore 64). I started with 8080 and Z80. The thing I missed when I started playing with 6502 were all the registers. On the Z80, HL for 16 bit source address, DE for 16 bit destination, BC for 16 bit byte counter then LDIR. I seem to remember being confused by all the addressing modes of the X an Y registers on the 6502. On the other hand, with Zero page addressing you have 256 8 bit registers. Maybe I just needed to spend more time with 6502 than I did.

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Roger Linhart
Portland, OR  97230
Mobile: 541-690-8560

[Phillip L Harbison]

Roger Linhart wrote:
> The thing I missed when I started playing with 6502 were all the
> registers.

You're supposed to use zero page as an extended register file.

> I seem to remember being confused by all the addressing modes
> of the X an Y registers on the 6502.

The index registers and indirect addressing are the best part!

> On the other hand, with Zero page addressing you have 256 8 bit
> registers.

The 6809 extended this by renaming this direct page addressing and
adding an additional 8 bit register to specify the upper byte of the
address. You could specify any of 256 pages to be your direct page. It
defaulted to 0 so effectively behaved like zero page. This was useful in
assembler code but I never found much use for it in my port of the QC
compiler to 6809.

> Maybe I just needed to spend more time with 6502 than I did.

This!

One advantage of the 8080 and Z80 was a clock that was 4x faster than a
6502, 6800, and 6809. That does not mean it was 4x faster, but memory
access times could be more granular.

--
Phil Harbison