On Sun, 19 Jan 2014 10:25:21 -0700, you wrote:
On Sat, Jan 18, 2014 at 7:36 PM, <sbell@...> wrote:
Are the Motorola ROMs subject to the same ROM rot problems as the notorious Mostek parts?
I have recently acquired a 7854 and it has a checksum error on power-up. I opened it up expecting to find Mostek parts but found it used Motorola parts instead. The Tek part numbers (with Motorola part numbers in brackets) are 160-0408-01 (SCM92210P), 160-0409-01 (SCM92211P), 160-0410-01 (SCM92212P) and 160-0411-01 (SCM92213P). The date codes are all mid '83.
I did repair one board with Motorola ROMs, but I don't know if it was
the ROMs or the FPLA that had failed.
Should I replace all these ROMs or are there other likely causes for the checksum error?
The ROMs & FPLA are the most likely cause.
I left the discussion of the FPLA (FPRP?) to others since I am not sure what it
could be replaced with and I believe with the right firmware image, the board
can be modified to not use it. My understanding is that it was used to patch
the mask ROMs with code stored in the 2716 EPROMs.
Since the FPLA uses NiCr fuse PROM technology which is very different from the
mask programmed Mostek ROMs, I have assumed it is more reliable.
Incidentally, Signetics called the 82S107 a Field Programmable ROM Patch. It is
obviously based on their 82S100 Field Programmable Logic Array but among other
differences, the -CE input is replaced with a -Flag output so instead of
responding to chip enable, it generates its own chip enable which is used to
drive other chip enables.
David Hess