Polymodular CPUs

[KA4HJH]

>> >The 6502 is still available in the US from Jameco Electronics. The 1mHz
>> version is $3.25 in single pieces.
>
>Not to take anything away from this fine CPU, but if a "start from scratch"
>design is decided upon, perhaps the 68000 should be considered instead?

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.

Terry Bowman, KA4HJH
"The Mac Doctor"