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Reading Atari Roms


IBP

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Not sure if this is the right place, so sorry if it's not.

 

I've just built a simple eprom reader for dumping atari carts. Now I don't know the first thing about how Atari roms are programmed, and so the root of my problem is probably something obvious I don't know.

 

I've assumed that the atari uses 4k roms, and hence address lines A0-A11, and based on pin outs of 2732 eproms I think I've worked out the addressing of the connector relative to the 2532 prom. I checked this against a pin-out of the atari cart connector I found online and it agrees with what I worked out (I know about the chip select being active high on a 25- series chip)

 

I can dump the first 2k - I have succesfully dumped combat and bowling carts, but 4k carts aren't dumped correctly. This suggests that I have some high byte addressing issues, but I can't find out what I've done wrong.

 

Has anyone else done this, and encountered (and solved) a similar problem?

 

Ok, on to bank switching. I assume that anything more than 4k is bank switched, given that I don't think there are more than 12 address lines. Is this the case, and so is Pole Position bank switched?

 

If so, once I get the 4k addressing sorted out, my reader should read a bankswitched cart, since I assume the bank switching cart hardware switches the high address bits to present 4k data streams at a time. This is transparent to whatever device is reading the cart, which should just pull in data as long as you let it.

 

Is this the case?

 

Thanks

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You should read Kevin Horton's sizes.txt, which has informations about the different bankswitching mechanisms:

 

http://www.tripoint.org/kevtris/files/sizes.txt

 

When you're trying to dump bankswitched carts you have to make sure you don't accidentally trigger a bankswitch, since bankswitches are usually triggered by accessing certain ROM locations (not always)

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Has anyone else done this, and encountered (and solved) a similar problem?Thanks

How are you dumping the chip ? are you using an edge connector and plug the cart in, or are you directly reading from the chip ?

 

When I first looked at a PacMan rom chip, i found that the pin assignment on the pacman rom is NOT identical to a 2732 EPROM.

 

The wiring on the PCB is such, that the right lines come out at the edge connector, but you can't treat the chip as if it was an EPROM. Here is the Pin assignment for a PacMan ROM:

 

Pin 1 to 17: same as 2732 EPROM

Pin 18: A11

Pin 19: A10

Pin 20: CE (A12)

Pin 21: OE (bridged to VCC)

Pin 22: A9

Pin 23: A8

Pin 24: VCC

 

You should use the edge connector to dump ROMs, not the chip. Custom ROMs may have any Pin assignment.

 

If you are already using the cart connector, can you please explain a bit better which problems you have. What do you read ? From a different location or rubbish ? You can easily compare what you read with existing ROM dumps.

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  • 5 weeks later...

If the second half is bad then you've messed up the highest address line. I seem to remember the online pinouts were wrong, ie the were for a 2k cart not a 4k cart.

 

For 8k banking I think they just read it twice, you may have to read it in both directions up and down. There really is no good way to do it because it's going to bank while you read it, so you will have to manually fix it.

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Sorry if this sounds ignorant, but why are you going through all this trouble to dump carts that have already been dumped and available for free download on this site?

Because it's there?

 

Seriously, though, the consensus is that the best 2600 cart dumper is a hacked 7800 console. I did my own a long time ago ( http://xi6.com/hacks/7800dump.html ), and if you google for '7800 devos' you should find the one that everybody else uses. They both substitute new code for the mostly empty ROM inside the 7800, and talk out a joystick port. The main difference is that mine does bog-standard 2400 baud RS-232 output, while devos requires a PC with a parallel port, which I ain't gonna find on my Powerbook.

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  • 1 month later...

i tried to make a cart dumper adapter using a catridge port from an old junk system. I wired it up like a 2732 like a previous poster said but it didn't work. I am probably overlooking something simple. the pinout on a cart edge connector, if you are lookig at it from the edge connector end with the label up, the top connectors are 13-24 from right to left, and the bottom would be 12-1, correct? i wired the port connector to a empty socket. I also found a differnt pin out for a 2732 here at this site-http://www.embeddedlinks.com/chipdir/pinusr/2732.txt. Which is correct or what am I doing wrong? does some one have any pictures of one that they made?

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The pinout on a cart edge connector, if you are lookig at it from the edge connector end with the label up, the top connectors are 13-24 from right to left, and the bottom would be 12-1, correct?

 

The consoles female connector looks like this, if you look at it from above:

 

1 ..........12

24 .........13

 

So I would think that if you look at the cartridge as you described, then you would see pins 1 to 12 from right to left on the top side and pins 24 to 13 from right to left on the bottom side.

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I wired it up the right way now but when I try to read a cart my programmer says it is not connected to the socket properly. if I try to read it with no cart in the port it doesn't see a problem with it. I am trying to use only 4k games like pacman and defender as i know it won't work with larger games.

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Just a clarification here: The meaning of the pins on the VCS connector is different from the meaning of the EEPROM pins. My picture above is only valid for the following meanings:

 

Top Row:

1(SGND) 2(VCC) 3(A8 ) 4(A9) 5(A11) 6(A10) 7(A12) 8(D7) 9(D6) 10(D5) 11(D4) 12(D3)

 

Bottom Row:

24(A7) 23(A6) 22(A5) 21(A4) 20(A3) 19 (A2) 18(A1) 17(A0) 16(D0) 15(D1) 14(D2) 13(GND)

 

 

Sorry if I confused you ....

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