5 Feb
2012
5 Feb
'12
11:47 a.m.
Next would be to sort the types out--try reading one.
Since they're
used, if they come up with some data, you can put those in the
"probably good" pile for each type. If they come up FFs, they might
be erased or simply bad. If they come up 00 or all the same pattern,
but not FF, those are probably bad.
A 'santiy test' I use when I'm dumping the contents of a ROM or PROM for
backup or simialr purposes goes like this :
1) Make usre every (used) data line is high sometimes nad low someimes.
Finding bout 00 and FF in the dump is a good start. Acutally, I try to
make sure that one data line is not exactly the same as another in all
cases.
2) Make usre all (used) address lines do something .Make sure there's an
even address such that the immediately-following odd address has
differnet contents (meaning A0 is significant), THen make usre there's an
address with A1 low such that the same address but with A1 high has
different contents, and so on/ Finally make sure the high and low halves
of the IC are differnet ;-).
The problem with these tests for unknown ICs is that there;s no way of
knowing which address and data lines were used in the original
application. For example, if the EPROM was a character generator for a
7-wire printhead, it would be reasoanble for one of the data liens ot be
either 0 or 1 all the time, it wouldn't have been used in the original
application. Of if an EPROM was used as a replaemetn for a smaller drvice
(say a 27128 used in place of a 2764), it would not be uncommon to
program the same data into the high and low halves of the IC.
But if the IC contains data (not all FFs) and passes those tests, it's
likely to be good. Most failures I've foudn relate to the circuitry
conencted to the pisn, so that, for example, an address input appears to
the stuch high or low.
-tony