Friday, 8 May 2015

Real CIA + CPU-Port-simulation

Now I found out that there exists a CIA in PLCC !!!
It's the 8520PL from the Amiga 600/1200. The only difference to the 6510 is that CSG changed the TOD to a 24-bit timer. But who need the TOD in the C64?

With the 8520 I can run the nearly unmodified KERNAL. The only thing I have to change is the PAL/NTSC detection, because I have no VIC and the KERNAL hangs in a screenline-read-loop.
I added a GAL16v8 that detected (together with A8-A15 from the GAL 22v10) the write to the CPU-port at $01 and stores D0 and D1 in two D-latches. The 16v8 gives LORAM/HIRAM to the adress-decoder in the 22v10.
Now I can turn off the BASIC and the KERNAL like in a real C64.
Also I burned Handic's MON-64 in the 32k-eprom before the basic and I can activate it by the EXROM-input of the GAL.
I wrote a small program (see below) to test the writing under the ROM, deactivating it and read from the RAM. - it wokrs !!!

No comments:

Post a Comment