Re: Commodore 64 Ultimate Cartridge project

Hi,

On Mon, May 07, 2012 at 06:00:24PM +0200, Michał Pleban wrote:
> Hello!
> 
> Working on several hardware add-ons for CBM-II made me thinking
> about doing a similar thing for Commodore 64. Specifically, an
> ultimate cartridge pack with the following:
> 
> * Small EPROM with bootstrap.
> * 16kB RAM.
> * SD card interface.
> 
> The bootstrap would load a selected cartridge image from the SD card
> into RAM, then reboot the computer to utilize this RAM as cartridge.

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:

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.

It's just a side note, that many devices (like real time clock) exists with
SPI bus, so many devices (SD card, the mentioned ethernet controller, the
real time clock) can be hooked on the SPI bus with seperated CS lines on the
microcontroller. This way it gives a great spectrum of purposes without
needing a too complex circuit anyway ...

Btw, the SD card and eth controller part was the major reason I've asked
about the user port on the list, I wanted to interface with an uC (where
some SPI devices connected to the uC), since I have not so much experiences
yet with using the cartridge port, shame on me :)


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