25 Jun
2006
25 Jun
'06
9:22 p.m.
Jules Richardson wrote:
what's the most sensible format for backing up PAL
chips such that they
can be recreated on a different system to that which they were backed
up on?
JEDEC fuse map and, if possible, logic equations. Strictly speaking though, a
JEDEC-format fuse map file is enough to copy a PAL. Equations just make it
easier to move to a different chip.
... some of which are presumably EPROM-only formats (I
don't have a
manual for the programmer)
Which programmer are you using? One of the Elan multipurpose programmers?
is there some sort of common format/size for PALs too
when reading (akin
to always being able to read a 27128 EPROM as a 16KB device regardless
of who actually manufactured it)?
Not to my knowledge. You have to get the programming algorithm right otherwise
you'll either blow the chip (literally) or get a garbage readback.
If you've only got one PAL, and it's not registered, map the circuitry so you
know where the inputs and outputs are. Build an adapter that converts a 27xx
EPROM pinout into the PAL pinout - connect the address lines to the inputs and
the data lines to the outputs. Read the chip out like that, and you'll get a
massive truth table of sorts. Take that and convert it back into the
equations, then compile it with OPAL or CUPL and burn a chip from it. Test
your new chip in the target circuit - if everything works, then you're done.
I'm concerned that this programmer
might be too old to have data on some of the PAL chips that I want to
archive - but if I'm only interested in archiving them (and so can set
the type to something of the right 'geometry' from a different
manufacturer) that's not necessarily that big a deal.
I'd be more worried if it was too new. A lot of manufacturers remove old
programming algorithms from their programmer firmware to make space for new
ones...
--
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