From: Marko Mäkelä (marko.makela_at_hut.fi)
Date: 2002-07-03 02:05:00
There was some discussion on the cbm-hackers mailing list on reverse
engineering the programmable logic arrays found in Commodore computers.
Simple formulae can be obtained by guessing from truth table dumps and
verifying the guesses with a program that transforms the logic equations
to truth tables that can be compared to truth table dumps from real chips.
Last night, I wrote the following two programs:
http://www.funet.fi/pub/cbm/firmware/computers/c64/pla.c
http://www.funet.fi/pub/cbm/firmware/computers/plus4/pla.c
These contain the logic equations for the C64 and plus/4 PLA,
respectively. Thanks to William Levak for providing me with the truth
table dumps.
By the way, does anyone know what the output F0 of the plus/4 PLA could
have been used for? It is '0' whenever the inputs I15..I0 are 0111 011x
1001 011x, and '1' otherwise. In other words, the signal is low
whenever the address is $fd2x and RAS is low and PHI0 is high.
Marko
Message was sent through the cbm-hackers mailing list
Archive generated by hypermail 2.1.4.