25 Apr
2009
25 Apr
'09
12:08 p.m.
On Apr 25, 2009, at 2:30 PM, Tony Duell wrote:
What about registered PALs? There are a great many of those
around. Figuring out the transfer function of a black box of
*sequential* logic isn't so trivial. :-(
-Dave
--
Dave McGuire
Port Charlotte, FL
It's even
more frustrating when you're looking at some CPLD or PAL
that's gone south. You don't have the original part to reverse-
engineer, the manufacturer is unlikely to furnish a replacement or
even the programming for the part. Usually, this means that your
widget is junk.
This is why I try to make backups of programmed parts while the
device is
still working. Of course some manufactures plow the protection
fuse, so
you can't easily read the device out (although for PALs, I believe
it's
always possible to deduce the logic equations with a bit of work
without
having to dump out the fuse map, there is no hidden internal state). A
suprising number of classic computers, though, have unprotected
PALs, etc.