Hallo allemaal, > On Fri, 2 Jul 1999, Nicolas Welte wrote: > > > > Hmm. now that I have worked out the bizarre implementation of the FM sound > > > chip on the 65xx bus, I doubt very much that a Soundblaster card could be > > > grafted onto the Commodore bus without at least some modifications on the > > > Soundblaster pcb. > > > > Why? The ISA bus should also have the separated READ and WRITE lines, > > and all the address lines are there. The interface to the SB card could > > be similar to the C64-OPL2 interface, with an added address encoder for > > the SB card. Instead of just decoding the C64 addresses to the OPL2 chip > > select you would have to create an ISA bus I/O address for it. Somewhat > > dependent of the R/W signals of course, because of that strange mapping > > on the Sound Expander. Doing it with discrete TTL components might > > actually be hard, but it should be possible to use some programmable > > logic like GALs. Not that I had any experience with them :-( > > Well I must admit I didn't know ISA had seperate read and write lines. In > that case, the decoding of the YM3812 on a Soundblaster is probably simple > enough not to get in the way of the 65xx bus. I'll buy a few ISA > connectors today ;) Basically, I/O2# has to be 'un-decoded' to appear as > 22xh on the ISA address bus. Assuming READ# and WRITE# are connected > straight through to the FM chip, they can be decoded in the usual SFX way > on the SB->C64 bridge card. > I once connected a MGP-card to my C64. The card disappeared during moving from one houde to another. If the sound blaster only uses I/O, one half of a 74LS39 will do the trick. Connect the PHI2-clock with input A and the R/W-line with input B. Output C reflects the needed WR-line, output D the needed RD-line. Connect the IRQ-input thru an invertor with IRQ5 of the card. The only thing I don't have a solution for is the DMA. You must hardwire the addresslines A8 and A9 so that the card sees the range $200-2FF. The AEN-line is connected to PHI2-clock AFTER it has been inverted. For those interested how I connected the MGP-card which needs RAM-addressing as well: I added a 8255. Two ports I used for A8..A19 and one line I used for telling it was an I/O- or Memory-operation. The other lines I used to read the IRQ-lines of the ISA-slot. These lines were connected to the IRQ-input of the C64 thru a NOR-gate. Groetjes, Ruud - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail email@example.com.
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