How to MAKE a "XX in 1" 8K games Atari 2600 Cart

[pcrock]

Hi friend. I own this cart with Two 8K games in (Ms. Pac Man  /  Donkey Kong Jr.).
To select the game you want to play you need to turn off and, after, turn on again the console.
The circuit uses 2 ICs (HCF4040BE and 74LS00BI) and a transistor that I think is a NPN one.
he Eprom is HN27128AG-25
My question is:
What will happens if I put a zif socket and try a 27C256 with four 8K games inside it or if i use a 27C512 with eight 8K games inside???
Would Work??
 

[ClausB]

That's some crazy shit right there! It does bank selection and also counts power cycles? Wow.

[pcrock]

14 hours ago, ClausB said:

That's some crazy shit right there! It does bank selection and also counts power cycles? Wow.

Yes. It is what it does.
But do you know the answer I asked for please???
If I change the chip with more roms inside, it will works???

[ClausB]

I don't understand that circuit. If you could trace the circuit and draw a schematic, then I could help.

[Kroko]

39 minutes ago, pcrock said:

If I change the chip with more roms inside, it will works???

Without looking at the circuit, I doubt that it will work. What the circuit has to do is to select the highest address line on the EEPROM to select one of two 8K areas inside your 16K chip.

If you want more than 16K to have more than two 8K games, you will need
 

* a larger chip which may have a different pinout => you may need some kind of adapter
* need a strategy to control the higher address lines because most likely your device is not doing this (you could use simple switches for that to set the high address lines to 0 or 1)

Then by cycling the power you would select between two 8K roms. By the switches you could switch in two different ROMs.

[ClausB]

Yes, switch selection would certainly work. But I wouldn't give up on that crazy circuit yet. It has a 12-bit counter which maybe could be used for those higher address lines.

[Kroko]

Can you find out (maybe with a multimeter) if the counter output is counting up on each power cycle ? I mean what the higher bits of the counter are doing ? ... do they count up or are they getting reset ?

Or maybe you have the time to reverse engineer the schematic for us

[pcrock]

1 hour ago, ClausB said:

I don't understand that circuit. If you could trace the circuit and draw a schematic, then I could help.

Unfortunately it is very difficult for me to trace the circuit...

[pcrock]

47 minutes ago, Kroko said:

Without looking at the circuit, I doubt that it will work. What the circuit has to do is to select the highest address line on the EEPROM to select one of two 8K areas inside your 16K chip.

If you want more than 16K to have more than two 8K games, you will need
 

* a larger chip which may have a different pinout => you may need some kind of adapter
* need a strategy to control the higher address lines because most likely your device is not doing this (you could use simple switches for that to set the high address lines to 0 or 1)

Then by cycling the power you would select between two 8K roms. By the switches you could switch in two different ROMs.

I plain to use 27C256 or 27C512. All of then appears to be compatible with 27128. Are this correct??

[+batari]

The '4040 chip is a 12-bit ripple counter so there are potentially up to 12 outputs here you might be able to use for the upper address lines of the EPROM to add more games.

 

Unfortunately, though, I don't think the games themselves are unmodified, as there is not enough logic there to support F8 bankswitching, so you would need to modify other games to work with whatever banking this supports.

[pcrock]

14 minutes ago, batari said:

The '4040 chip is a 12-bit ripple counter so there are potentially up to 12 outputs here you might be able to use for the upper address lines of the EPROM to add more games.

 

Unfortunately, though, I don't think the games themselves are unmodified, as there is not enough logic there to support F8 bankswitching, so you would need to modify other games to work with whatever banking this supports.

Thanks for replying.
I don´t know to modify Roms to do that. I think what I want to do is a bad idea so...
Even If I use an other 27128 to use only two games and to burn 2 any 8K roms inside the new chip it still will not work if the roms need to be modified...

[Danjovic]

Word "solda" on the board delivers the this is a cartridge from Brasil. You can also see missing diodes, probably part of decoding logic left aside.

There is a chance that you can combine the counter and the logic to have a standard bankswitch. If you can get the eprom out and read you can compare the binary with the original games and check if the bakswitch is a standard one or if the games were hacked.

If you ever dismantle the board to investigate that, please take some pictures and post here so we might trace the circuit.

[pcrock]

11 hours ago, Danjovic said:

Word "solda" on the board delivers the this is a cartridge from Brasil. You can also see missing diodes, probably part of decoding logic left aside.

There is a chance that you can combine the counter and the logic to have a standard bankswitch. If you can get the eprom out and read you can compare the binary with the original games and check if the bakswitch is a standard one or if the games were hacked.

If you ever dismantle the board to investigate that, please take some pictures and post here so we might trace the circuit.

Yes friend! That is a Brazilian cartridge. Here in Brazil, due the parts costs, there were a LOT OF TRICKS to turn the things cheap!! Here we have things like four 8K games in a 27128 chip (as posted in another post) and more!!!
I WILL TRY remove the chip from PCB and post some pics here!!!
Thanks for replying.