Fw: [sdiy] Anybody using Atmel AVR?

[Roy J. Tellason]

On Thursday 23 December 2004 11:21 pm, Phil Harbison wrote:
> Roy wrote:
> > Yeah,  but when these days would you possibly want to
> > impose any wait states on one of those chips? [...]
>
> These days I would not use those parts in a new design,

I wouldn't,  if it were a matter of going out and buying a bunch of chips, 
particularly if I were going to manufacture something.  OTOH,  I do happen to 
have a bunch of these on hand,  and thought it'd probably be kinda nifty if I 
could get some use out of them...

> but we were using them in 1979. We never had a problem finding static RAM 
> that could keep up with a 1 or 2MHz 6502. The problem was dynamic RAM.

>From the standpoint of wanting to make some simple little circuit,  that's a 
problem all right!  :-)

> What do you do when you need to refresh the RAM? It is fairly easy to piggy-
> back a refresh cycle onto every memory cycle (and the Z-80 would even do
> this for you) but not very practical if that means doubling the duration of
> each memory cycle.

Most of the stuff I saw designs of time-sliced it.  Combined memory access for 
the CPU on one half of the time allowable with memory access by the video on 
the other,  which by definition would cycle through a whole range of 
addresses.  Some of the web pages I've seen dealing with this and other chips 
seem to involve some of the same kind of thinking,  where people are building 
whole small general-purpose computers out of these parts.  When it comes to 
that I really can't see the point,  since if that's all you want there's 
plenty of them around,  free for the asking in many instances.  My possible 
uses of such stuff is likely a whole lot smaller,  a whole lot more 
specialized,  and won't include video.  :-)

> But I was thinking more about the CPU implementation. If you are 
> implementing those complex addressing modes it would be nice to have more, 
> shorter clock cycles per instruction since it probably doesn't take a 
> microsecond to add a base address to an index register.

I've heard of people doing things like putting a "6502 core" into a 
programmable chip (FPGA?  I don't recall) and running with clock speeds in 
excess of 20 MHz.  Fast enough for you?

> Roy J. Tellason wrote:
> > So what fun sdiy things can we do with them? [...] but I
> > have *lots* of 6502-family stuff,  including the cpu,
> > 6510 cpu,  6522,  6526,  6551,  etc.
>
> IIRC, the 6522 had a shift register which I always thought
> could be used to build a primitive LAN or control bus. You
> might build an array of voice cards (each with a 6502, 6522,
> EEPROM and RAM) controlled by a master 6502 with MIDI I/O.
>
> > and also the same with z80-family stuff...
>
> ACK!!! Torment me not with the Z-parts!

Hm,  didn't see this post (yet?)...