4 replies to this topic

[Susuwatari]

Since I wouldn't be able to do anything with my planned 8K multicart until I get those NAND gate, I decided to look elsewhere. O^2 was the first thing that popped in my vision and since there's no documentatuion on such multicart, I'd thought I'd tackle this one. There are reference to a multicart but it seems like vaporware on the internet.

It was like pulling my teeth just to get *any* technicial docs on O^2. And the best I got was the cart pinout so I had to trace to the chip and find what pin are for what. To my surprise, O^2 cart is nearly 100% compatible with EPROM pins. Just 2 minor differences plus a change with EPROM's VCC pin. Actually I shouldn't be surprised at all, O^2 AV mod was insanely easy as well as controller port mod to make it compatible with 2600 controller.

I haven't built a multicart so no guarrantee it'd work. it is just a theory that looks good on paper.

There are 2 basic ^2 cart design: 2K and 4K. 2K doesn't have any P11 line and adding a wire from the cart connector to the EPROM could be messy so try for the 4K cart. No 8K cart was commercially made so you can ignore the need for P10 line.

I'm going to use 2Mbit EPROM for reference (since the *entire* O^2 ROM library can fit). You can use 1Mbit EPROM but only about 2/3 of all O^R ROM could fit. Desolder and remove the old chip. You could install a socket if you want. Make note of where the chip's notch was. The notch of the EPROM (or socket) is on the same side of the PCB as the original chip but pin 1 doesn't go in pin 1. Pin 5 of the EPROM goes in hole 1 of the PCB.

Lift pin 22 of the EPROM (or socket) and connect that to ground (hole of pin 12 on PCB) Lift pin 25 of the EPROM and add a jumper to hole of 18.

Lift pin 28 of the EPROM, that will go to DIP switch 2. Connect pin 31 and 32 to hole of 24 (VCC). 29 goes to switch #3 and 30 to switch 6 (NC on 1Mbit EPROM)

pin 4 of EPROM to switch #1, 3 to SW 4, and 2 to SW 5. Finally, pin 1 of the EPROM should be grounded I(you know where it is?)

like with Atari 2K/4K multicart, you'll need to double up all 2K ROM (use copy /b game.bin+game.bin game4k.bin in DOS box) Then combine all the 4K ROMs in the order you want on EPROM.

I'll post later when I get around to building it. I'd appreciate feedback from O^2 experts (especially if P11 line behaves like normal address line or not)

Future plan could include menu driven selection but I have no experience on programming O^2. One plausiable way is to use the unused P10 line to send clock pulse to a binary counter (like a 7493 4 bit binary) and binary counter could be connected to the higher address line of the EPROM. Then restart the machine so it'd behave as if you just inserted the game cart. I don't know how this can be done since there's no software reset (reset button is not software controlled)

[ozyr]

look at http://www.classicgamecreations.com/ for a current 128-1 multicart that was finished a few months ago! Great cart, but I do wish it was menu driven!

[DanBoris]

If you need tech info on the O2 check out by O2 Tech Manual at: http://www.atarihq.com/danb. Also check out: http://soeren.informationstheater.de/

There where a number of 8K games released, Killer Bees, Popeye, Qbert to name a few.

Looking in my notes I found this information about an old O2 multicart someone build:

Using a 27C040 EPROM, connect the pins as follows

Pin O2 signla
1 Dip switch
2 Dip switch
3 Dip switch
4 P11

32 +5
31 Dip switch
30 Dip switch
29 Dip switch
28 Dip switch
27 A8
26 A9
25 A10
24 PSEN
23 A11
22 PSEN

I didn't document the other pins, so they probably connect to the standard signals for an EPROM.

You could easily do automatic bankswitching by using a latch IC instead of a dip switch. You could enable the latch using the P14 (pin 11) on the cartridge. You would then put your game select program in the first bank and make sure that bank come up at power up.

Dan

[Susuwatari]

DanBoris said:

If you need tech info on the O2 check out by O2 Tech Manual at: http://www.atarihq.com/danb. Also check out: http://soeren.informationstheater.de/

Thanks for the link. It seems Atarihq.com is down.

Quote

There where a number of 8K games released, Killer Bees, Popeye, Qbert to name a few.

And Turtles. Killer Bees and Turtles seems to be the only NTSC O^2 game that are 8K. I'll skip them.

Quote

Looking in my notes I found this information about an old O2 multicart someone build:

Using a 27C040 EPROM, connect the pins as follows

Pin      O2 signla
1        Dip switch
2        Dip switch
3        Dip switch
4        P11

32      +5
31      Dip switch
30      Dip switch
29      Dip switch
28      Dip switch
27      A8
26      A9
25      A10
24      PSEN
23      A11
22      PSEN

I didn't document the other pins, so they probably connect to the standard signals for an EPROM.

That pretty much matches my work except for A10 and A11. I had mine as EPROM A10 to O^2 A11 (O^2 doesn't have A10 on cart port) and EPROM A11 to O^2 P11 (for 4K bankswitch) I'd have to experiment and see which works.

Quote

You could easily do automatic bankswitching by using a latch IC instead of a dip switch. You could enable the latch  using the P14 (pin 11) on the cartridge. You would then put your game select program in the first bank and make sure that bank come up at power up.

Dan

That's also possible if I wanted to support all ROMs including 8K games. Since I'm going to stay with 2K and 4K only, I could use P10 on O^2 cart (normally it's for 8K bankswitch select but it can be connected to ROM selector circuit.) Or I could use P14 since none of the O^2 cart seems to use that anyway. Software menu selector is still a while away as I'd need a programming lesson or someone who can program it.

[DanBoris]

Atarihq.com keeps having DNS problems, it will come and go.

The "25 A10" was a typo, it should have been "25 P10" which makes more sense. A10 is missing from the cart connector because memory locations $0-$3FF are the internal processor ROM, and the cart ROM starts at $400.

I remebered after I wrote that, that P14 is used to control the Voice module. So if you want to do voice games, P14 wouldn't be a good idea for controlling bank swithcing.

Dan