Re: Commodore 64 Ultimate Cartridge project

From: Michał Pleban <>
Date: Mon, 07 May 2012 18:25:29 +0200
Message-ID: <>

Gábor Lénárt wrote:

> I also thought about it, since I've started to play with interfacing with SD
> card on SPI bus, currently only through PC parallel port (to "play" with it
> and some studies for myself), but I'd use a microcontroller with dedicated
> SPI capability (btw, I also thought about using ECN28J60 which is a 28-pin
> SPDIP ethernet controller with SPI bus - it's really cheap, and not so slow,
> even 20MHz SPI connection is OK for it -, maybe easier to play with it for a
> hobby user like me, without heavy SMD, etc soldering and PCB designing
> capaibilities).  One question came into my mind however: I would hate to use
> an EPROM just for bootstrap.  It would be interesting to see this works:

Well, I don't want to use any microcontroller for the simple reason that 
6502 is the only processor I know how to program :-P

> let's call the program of the microcontroller as "firmware". Now, the
> firmware would contain some C64 code as well, if C64 needs "bootstrap". The
> microcontroller on RESET can read it from code memory and write into the
> RAM. This way, an EPROM is not needed. Just I am not sure it's possible as
> the time is too short to do this on power up (I mean the C64) and the
> microcontroller is not ready yet with the copying; but I guess it's possible
> to stop 6510 (by the uC) till it's done.

Perhaps you could use the /DMA line to stop the CPU on reset while you 
are initializing stuff.

But all this is too complicated for me. Two processors sharing the same 
RAM, bootstrap for 6502, bootstrap for the microcontroller... it gets 
nasty. I like simple solutions:

* C64 boots in Ultimax mode from 8k EPROM.
* The EPROM bootstrap reads whatever it needs from the SD card and 
initializes the RAM.
* The RAM can be loaded with a pre-chosen cartridge image or with a menu 
program to choose another cartridge. Or just with nothing at all to 
start the computer normally.
* The bootstrap code disables Ultimax mode and reboots the computer.


       Message was sent through the cbm-hackers mailing list
Received on 2012-05-07 17:00:40

Archive generated by hypermail 2.2.0.