Re: Blank CMS SCSI Card PCBs

[david@uow.edu.au (David Wilson)]

"nic" <heel@ifrance.fr> writes:
>The bit security is only a way to prevent people to do a dump directly  the
>content, of course if you test all the combinaisons of the pal, you would
>know the fonction release by the pal or gal but it take a long time to do it
>and then you have to use a coder (samll software) to create the dump.
>Very often they are use to do an adress decoder in one chip instaeda of
>using two or three 74ls138.
>When the bit security is on you only get FFhex or 00hex value when the
>burner do the dump.  it will not destroye the ship.
>But of couse you have to unsolder the pal

The security bit does not really help if the PAL is a simple combinatorial
circuit. It does make a difference if the PAL is registered or has feedback
connections. If we look at a 16R8 we find that it has 8 inputs and 8 i/o pins
(plus a clock pin and an output enable pin). This means that it has 256
states it can be in and with 256 input combinations we get 65536 combinations
we need to test BUT we can only apply 256 different inputs to test it.

It can be very difficult to test all the transitions without a way of
setting the output pins to a particular state.

P.S. I have built the hardware (soldered a ZIF socket to some ribbon
cables that I soldered to the back of a simple 6821 based printer card I have)
and am now working on writing the softare to scan all the input states.
I have found a program in an old Electrical Engineering textbook which
appears to be able to convert a truth table into an equation - unfortunately
it is written in Algol 60 and I will have to find a C version or convert it
myself.
--
David Wilson  School of IT & CS, Uni of Wollongong, Australia