newbie building a scratch-built computer - test-drb@ccmp.vtda.org

5 Aug 2007

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Subject: Re: newbie building a scratch-built computer
   From: "Holger Veit" <holger.veit at iais.fraunhofer.de>
   Date: Sun, 05 Aug 2007 12:23:15 +0200 (CEST)
     To: "General Discussion: On-Topic Posts Only" <cctech at
classiccmp.org>

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. 
Neither have I.  I have 2716s, 2732s dating back to early 1980s that 
have seen many cycles in many many projects and they are still good.
The thing that seems to kill Eproms is excessive erase times and 
reverse polarity.

Allison

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*) 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...

-- 
Holger 