How exactly do PAL chips get programmed?
jwstephens at msm.umr.edu
Thu Nov 17 17:25:38 CST 2005
Teo Zenios wrote:
>So if I have the original code and know what chip it needs to be programmed
>on I might be in luck, otherwise there is little hope?
>Are PAL's or GALs expensive to get? Do people here have access to
<excellent replies snipped>
If you have a chip which you doubt is functional, it may still read out
it's fuse map.
The fuse map of say a 22L10 or such may be perfectly readable even if
is not playing in the circuit. One thing that went bad on them was the
fully drive the loads in circuit to ttl valid regions. IIRC this would
be < .7 for low,
or > 2.2 for high. (for the sake of argument). When you pull the part
and put it in
a programmer, the loading is much more friendly, and the programmer may well
pull a copy of the fuse map unless the security fuse(s) are blown as
by tony D.
For historys sake, the PAL's were programmed originally with a tool
and later by lots of other tools. The fact that the security fuse could
meant that you had to have a way to determine if your device was
was supplied in a proper environment by supplying a "model" which would flip
the lines according to function of the device and test it, after the
programmed, to show that it was good.
Most engineers I ever worked with, and in the organizations I saw, few
ever done but to save the PALASM source, (or whatever source) and the
fusemap. If the engineer ever bothered to use the model and simulation
and specify that, I never saw it. They usually would blow a pal, test
it in the
circuit, and when it worked, save the source and ship the fusemap out as
thing to manufacture by.
Anyway to connect back up, what is malfunctioning, and why do you think the
pal's are bad? I didnt see a reason why that is suspected, or how you could
have found that out. I must assume you have a schematic to have figured
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