Re: Designing the Ulti(mate) MAX cartridge

From: Steve Gray <sjgray_at_rogers.com>
Date: Wed, 19 Dec 2012 09:25:54 -0800 (PST)
Message-ID: <1355937954.6979.YahooMailNeo@web161306.mail.bf1.yahoo.com>
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
>
>
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Received on 2012-12-19 18:00:11

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