backing up PAL chips

Tony Duell ard at p850ug1.demon.co.uk
Sun Jun 25 17:58:35 CDT 2006


> 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)?  I'm concerned that this programmer might be too 

NO!. In fact you can ruin the chip by getting the manufacturer wrong!.

There is a big difference between a PAL and an EPROM in this respect. 
When an EPROM is used in the normal application circuit, it is read out, 
and what you read out is simply the pattern of bits that you programmed 
into the device. But when you use a PAL, you don't read out the fuse map 
(think about how a PAL is actually constructed). 

To read the fuse map out of a PAL, you have to get it into a 
program/verify mode. Typically, this involved overvoltaging one or more 
of the pins. Needless to say, if you get this wrong (and different 
manufacturers did their own thing, many of them refused to document the 
method except under an NDA :-(), you will damage the chip. 

-tony




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