newbie building a scratch-built computer

Holger Veit holger.veit at
Sun Aug 5 05:23:15 CDT 2007

Tony Duell said:
> IMHO, more important than the EPROM programmer is an EPROM emulator. This
> is a box of RAM that connectes to the EPROM socket of the target system
> (the board you'be just made) and also to a host machine (PC,  parallel
> port, serial port, USB?). YOu can quickly download perogams into the
> emulator, which then appears exactly as the EPROM does ot the target, and
> the latter can therefroe run said programs.
> The advantage over using EPROMs is that you can re-write the RAM as many
> times as you like (EPROMS have a limited number of program cycles) and
> rewrite it quickly. Unless your programming is a lot better than mine,
> you will go mad if you have to wait 20 minutes for an EPROM to be erased
> and reprogammed. each time you want to make a change!

I haven't so far reached the maximum # of programming cycles for EPROMs in
any experiment. *) As I recommended you might use EEPROMs instead of
EPROMs mainly because of their moderate capacity (you won't need PC FLASH
ROMs with 1MB or more for an 8 bit system) and because they don't need
erasing in the UV coffin.

*) Maybe your and my programming strategy differs; now with SW emulators
for almost any old CPU being available ona PC, I tend to test my code in
an emulator, often with single stepping first before I make a HEX file to
burn it; even with EEPROMs - the old turnaround cycle of change a byte,
program, insert and test how far it works is still too long even with RAM
boxes. Admittedly, in the old times, without PC emulation, I did a lot of
paper testing work first before burning the stuff into an EPROM; this
discipline meanwhile degraded...


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