Polymodular CPUs

[Karl Helmer Torvmark]

KA4HJH wrote :
> The 68K is a great processor but below a certain "horsepower" level
> complete overkill. How much do you really need? If a 6502 (best 8 bit
> processor of all time) can handle it, well...
> 
> Another thing to consider is whether you can get by with a single-chip
> design or need an extended architecture controller (with external RAM,
> E(E)PROM, memory-mapped I/O, etc). Single-chip is much simpler and less
> expensive to build but potentially more difficult/expensive to develop, as
> you may have to buy an pricey development system. Extended is easier to
> devolop in-circuit if you have an I/O port and a debugger in firmware.
> Single-chip designs often fit on a single-sided PCB. Extended almost always
> requires at least two layers.
> 
> One recent development in favor of single-chip is serial EEPROM. You can
> save configuration data in non-volatile memory using only one or two I/O
> pins. Where was this years ago?
> 
> And there are lots of cheap single-board controllers available these
> days--pick your processor.

I would heartily recommend that any new projects use modern controllers.

If you look at the Atmel AVR for instance, you have a flash-based
controller (no more expensive "window" development kits, OTP-based
controllers are really not suitable for DIY) with plenty of on-chip
pheripals (sp?) and you can choose from everything from a part with 1K
program memory, no RAM, and only one timer to a chip with 128K program
memory, 4K of RAM, 4K of EEPROM, 3 timer-counters, 8 channel 10-bit ADC,
up to 48 I/O pins, possibility of adding up to 64K of external RAM,
and 3 PWM outputs.

Development kits for these chips are cheap, and are available from several
vendors. In addition, they are in-system programmable, just include a
6-pin header and the right connections on your board. Compared to a
solution with the 8051, 6502 etc. you have a complete one-chip solution
for what would easily require a handful of circuits to implement with the
older controlllers. There are several freeware compilers and assemblers
available for the AVR as well.

BTW, (shameless plug alert) if any of you are interested in AVRs, have a
look at the resource page me and some student buddies of mine made at 

http://www.omegav.ntnu.no/avr/

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Karl H.