Well, if you look at the 6502 architecture very carefully, you'll see what a
thing of beauty it really is. What the 8080 and Z-80 designers did with
brute force, the 650x designers did with resourceful elegance. Instead of
big counters and the like, for, say, the stack pointer or the program
counter, the 650x needs only to use registers. The same ALU that is used in
the execution of instructions is useable to increment the program counter,
manipulate the stack pointer, etc. The part can be built with extremely
little in the way of resources. I once sat down with a pencil and figured
out that you could build the content of the 6502 with a pair of 74181's, a
pair of 74189's four '373's a couple of decoders, a small PAL and a 256x12
rom (3 82S129's) That was all available in '75 or so, with the possible
exception of the PALand the 373's. That is not very much logic. That was
possibly what they used to prototype their part.
Think about it! It's really simple and you could easily build it as part of
a gate array. Try that with a Z-80 and see what you get.
Dick
-----Original Message-----
From: Allison J Parent <allisonp_at_world.std.com>
To: Discussion re-collecting of classic computers
<classiccmp_at_u.washington.edu>
Date: Sunday, April 11, 1999 6:08 PM
Subject: Re: stepping machanism of Apple Disk ][ drive (was Re: Heatkit 51/4
floppies)
><I'm not sure I'd agree, when it comes to indexing. I think the 6502
><indexing is more useful in typical cases, and the instruction set is much
><"cleaner" in some ways. However...
>
>it has to be as there are so few register to store intermediate results or
>addresses. The end result is operands are out in memory more and return to
>memory more. Different optimization of resources.
>
><Exactly. I was brought up on the Z80, or at least that's what my earliest
><assembly language experience was on, but I learned how to use a 6502 prett
><well. Just a different design philosophy.
>
>the oder of learning for me was PDP-8, PDP-10, CM2100, 8008, 8080 then
>over a span of 6 years. From the 1975 to 1978 the list is z80, 8048,
> 1802, sc/mp, 6800, 650x, 9900, pdp-11!
>
>I have fewer biases. ;) Well ok, if said 8085 for some, 804x for others,
>T-11 (pdp-11 on a single chip), and z80. Never had more than the few 6502s
>until recently but they are fun too.
>
>Allison
>
Received on Sun Apr 11 1999 - 20:40:12 BST