>>> The row address is the low-order 6 bits, right? >> >> Low eight on the VIC-II in the C64 (there is a mask option to make >> it low seven, to work with 16k DRAM chips). > > Right, low 8 on the VIC-II, but I was thinking of the 4164 memory > chips. Those have eight address pins, which is the row (low) address during #RAS, and the column (high) address during #CAS. >> Here's my PLA decode for Ultimax mode: > > Thanks. FWIW, Jens Schönefeld posted the C64 PLA truth table on > German Z-Netz in the autumn of 1994. He had built an adapter that > makes the 82S100 PLA look like a 27512 EPROM. I got it from the net, sure. The one that is all over the place is WRONG (there is a line missing), but someone noticed and posted a new one :-) > Back then, I managed to reverse engineer the equations for all > signals except CASRAM, which remained too complex to be plausible. #CASRAM is mostly "if not X and not Y and not ..." > Verification was by a program that computes the truth table by > feeding all 65536 input combinations to the 8 equations, and by > comparing the resulting 64KB file with the PLA truth table dump. > > Some time later, it turned out that the PLA does support negation, > and the CASRAM equation became a lot simpler. The file on Zimmers, > which I originally archived on FUNET, is dated July 1995: http:// > zimmers.net/anonftp/pub/cbm/firmware/computers/c64/c64pla.txt > If I remember correctly, I sent the chip to be read. It was from my > oldest C64, serial number 32xxx, with ceramic DRAM chips (350ns > IIRC) and 6569R1 and so on. An antique! Segher Message was sent through the cbm-hackers mailing listReceived on 2011-12-08 15:00:08
Archive generated by hypermail 2.2.0.