C64 and plus/4 PLAs revisited

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:


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.


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