The A/V module was what sort of inspired me, though I had been thinking
about something like it for a while. You do have to cut the A12 trace
on the board and run a wire to daughter board from the cartridge
socket. This is because A12 is used as a chip select for both the
cartridge (when it is high) and for the TIA and RIOT (when it is low).
They have to be seperated to make the rest of the data space usable.
I do plan to make this available with a real PCB eventually. Plans
include a way to download ROMs over the RS232 port, though as usual, I
am sure the bankswitching stuff will be tricky. Max speed for the 6551
asych communications interface is 19,200 baud, though I think I can
sacrifice adjustable baud rates for a fixed higher baud rate of up to
125,000 baud.
As for how to use the RAM, it is pretty wide open. From using it for
video memory, or unloading a banked cartridge, or just downloading a big
game to it directly over the RS232 port (or maybe a USB...).
My next step is to get the RS232 portion working, followed by the basic
boot ROM (probably 8K). I may also include some common subroutines,
such as vertical sync, counting, basic drawing stuff, just to save room
in the cartridge.
-Billy
Glenn Saunders wrote:
Very impressive.
Maybe someone can combine this with the Cybertech A/V mod (there
probably isn't enough room for both to coexist separately) and offer
it commercially. It's just a drop-in daughtercard that goes into the
6507 socket, right? It doesn't require any jumper wires? The cart
port is still pretty much the same, right?
I guess you are planning to write the boot-loader so you can load
games directly through RS232 rather than cart. Since 32K linear RAM
is a nicer memory model to work in I'm assuming that if you wrote a
game on cart you'd probably want to store the game like a file in
banked ROM and have a loader routine copy it all to RAM and then jump
into it.
Plus, with the RS232 then you could write a simple client-server app
on the PC that could read and write files on demand for the 2600,
which could also be used in mid-game for levels, high-score saves, etc..
You could write a pretty massive RPG that way.
I know you can still do something like this by sacrificing a joystick
port by using a Cuttle Cart/SC but you just can't hold much RAM at a
time that way so you'd be requesting loads pretty constantly.
How fast do you think the serial could go with the stock 2600's 6507
clock speed?
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