Hi Rob, Glad you like my mod! This is a great idea. I think you might find some ideas in Eslapion's Behr Bonz cart for the VIC-20. He made the schematics available. Not sure where they are on the web now but if you need them I have them archived. Steve >________________________________ > From: Rob Clarke <crock@clarke-family.org.uk> >To: cbm-hackers@musoftware.de >Sent: Wednesday, December 19, 2012 11:55:31 AM >Subject: Designing the Ulti(mate) MAX cartridge > >Gentlemen, > >Thanks to Steve Gray’s simple MAX machine modification, I now have my MAX >working via composite out to my LCD TV. Despite having ipad’s, Nintendo >DS’s and a Wii, my kids spent hours playing the ultimax mode cartridges >which is testament to the playability of the very earliest games from HAL >labs and the other stuff produced in Japan. > >Given it’s one of the rarer of my Commodore machines, I didn’t >particularly like the idea of my 6-year old Son swapping the cartridges >himself so it got me thinking that it would pretty easy to make an ultimax >mode cartridge which would boot into a menu and allow the user to select >an image with the joystick. As there was only a total of about 30 ultimax >compatible games (and even then, several of these were different versions >of the same game), they would all fit onto a 256k x 8 prom. I know there’s >several solutions that do this for the stock 64 (easyflash, alienflash, >u1541 etc) but none work on a max machine as far as I know and, besides, >this is more an exercise to see if I can. > >Although I’ve spent a few years on the forum, I’ve never done much >hardware hacking myself, mainly just for repairing and knowledge, so I >wanted to run a couple of ideas past you guys to see if they’re workable. > >If I assume I’m using a 2mb prom, which would hold up to 32 x 8k images, I >need to find a way to programmatically control A13 -> A17. My idea was to >use a tri-stateable latch such a 74LS373 which I would latch with one of >the chip selects on the MAX expansion port. Pin 7 controls /EXRAM which I >think is only used by the MAX-Basic cartridge. I haven’t checked, but I >assume this maps to $0800-$0FFF, so I can latch these address lines with a >write to an address in this space, AND’ing this with the R/W line. If I >copy a small banking routine into the RAM at $0000-$03FF, I can set the >latch and JMP ($FFFC) to start the image. This will all come a bit unstuck >if the image makes writes to the $0800-$0FFF address space but the only >image that would do that would be the MAX-BASIC, which I would not >include. > >This leaves the problem of how to ensure it comes up properly when RESET. >My idea with the tri-stateable latch was that I could pull-up (or down) >the banking address lines with a resistor pack and control the output >enable with another line exposed on the MAX cartridge port. What this line >might be is more problematic. On the MAX schematic on Zimmers, I notice >that P2 of the 6510 I/O port is exposed on pin-22 through a 470ohm >resistor. On a 64, this would be ground, but maybe I can use this to >control /OE on the MAX? This raised another questions though which I might >have asked before on this forum which is: > >Q) When a 6510 is reset, what’s the default state of the DDR and I/O ports? > >The answer I am hoping for is that they are set for input so that I could >have a pull-up resistor on /OE up to disable the latch outputs and rely on >the pull-ups on the address lines to bank in the correct menu image when >RESET. The worst answer would be that it’s not deterministic at all, in >which case it would be very difficult to use P2. If this will not work, I >am open to suggestions as to an alternative. If I used an octal latch like >the 673 I would still have 3 unused with a 2mb PROM so I wonder if I >could use some nasty feedback option where I use one of the unused latches >to control its own output enable. If I then use /EXRAM to control /OE and >(inverted) LE, writing a 0 to the latch would enable it and a 1 would >disable it. > >Could these ideas work or am I talking garbage? Don’t feel bad about >tearing my ideas apart. > >Cheers, Rob > > > Message was sent through the cbm-hackers mailing list > > > Message was sent through the cbm-hackers mailing listReceived on 2012-12-19 18:00:11
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