[H-GEN] Vintage computing mystery

Russell Stuart russell-humbug at stuart.id.au
Fri Feb 2 16:46:24 AEST 2018


On Fri, 2018-02-02 at 16:14 +1000, Arjen Lentz wrote:
> So with that info, you'll be able to figure out what the circuit does
> with what the CPU code puts into the PAL.

PAL stands for "Programmable Array Logic", which is what one used
before FPGA's came along.

Anyway the point is they are programmable, meaning you have no idea
what they do until you see what they were programmed with.  If they
haven't blown the read bit you could read the program out.

In a past life I used one to as a form of copy protection on a memory
board.  The CPU software would feed it a string of bits and see if it
computed the function it was supposed to.  If it didn't the software
would refuse to use the memory.  We blew the read bit of course. 
Naturally the memory was expensive as you would only buy it from us.

Some electrical engineering students later told us after seeing the
price they thought they would be able make some quick holiday money
selling similar board cheaply.  That's when we learnt the PAL paid for
itself.


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