Den Tue, 20 Feb 2018 22:17:16 +0100 skrev didier derny <didier@aida.org>: > frankly I just bought a cbm 710 board and was thinking to try to make > adapter > > something like 6502 + cpld > > in the cpld the code to trap the 2 opcode sta ($addr), y and lda > ($addr),y using sync > > normally one of the registers 0 or 1 I dont remember (execution) is > always on the bus > > the second is inserted temporarily during these instructions... This seems to be rather straight forward. > I'm thinking to a replacement for the 6525... I'm looking for them, > hard to find :( Unfortunitely it seems like the CBM-II/B-series uses one of the 6525's in the mode where it acts as an interrupt controller. Port A and B can probably be emulated with an 6821 or similar, or even with simple hardware registers for those signals that's always used as either input or output. Fortunitely CB isn't used and CA is used as a simple output used to control something in the video generation hardware. I assume that there are no software for theese computers that use every single feature of the hardware (like demos on C64), so it might be possible to get away with a partial emulation of a 6525. The other 6525, used for keyboard scanning, seems to be used in it's simple tri port mode, and could probably be emulated by some really simple hardware. A way of cheating would be using some other kind of hardware and patch the Kernal, but then you could argue that it's not even a Commodore B series replica at all. Btw I had a look at the P500 schematics. Theese parts seems rather similar. In general I don't understand why it has both 64K DRAM and 1k SRAM (plus 1K nybble color ram) connected to the VIC-II? It seems like the 64k DRAM is only available in page 0 while the small SRAM is available in page 15 too. That would partially make sense if there were any coprocessors for the P-500, but I've only heard of the 8088 card for the B series. But it doesn't really make sense even with a coprocessor as the 64k DRAM for page 0 is hooked up in a different way than the rest of the dram, making page 0 available to the 6509 (and VIC-II) even with another processor using ram page 1-3. Maybe they just had bad luck when they made the design, or they had problems getting the dram page 0 to be stable and added the 1k sram as a temporary solution, never fixed? :) -- (\_/) Copy the bunny to your mails to help (O.o) him achieve world domination. (> <) Come join the dark side. /_|_\ We have cookies. Message was sent through the cbm-hackers mailing listReceived on 2018-02-20 23:00:56
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