How to make 4kB EPROM cart (Atari 2600) from the old one

[ClausB]

If you have already modified the board as above, then cut the bare wire to pin 21 and jumper a new wire from 21 to 24 as below. If you have not yet modified the board, then do not cut the trace between 21 and 24 and do not add the bare wire to pin 21.

 

[pcrock]

On 03/08/2020 at 20:48, ClausB said:

Prenda o pino 21 no pino 24, não no fio desencapado da foto.

Thanks a lot!!! I will try it and later post the results!!

[pcrock]

On 04/08/2020 at 17:29, ClausB said:

Se você já modificou a placa como acima, corte o fio desencapado no pino 21 e faça a ligação em ponte de um novo fio de 21 para 24 como abaixo. Se você ainda não modificou a placa, não corte o traço entre 21 e 24 e não adicione o fio desencapado ao pino 21.

 

So... Jut like originally was???

[ClausB]

Wow, I didn't know I could write Portuguese! Not well though - I don't seem to be making myself understood.

 

Yes, leave pin 21 as it was. Of course you still need the other cuts, the inverter chip, and the yellow wires as shown.

[pcrock]

On 8/4/2020 at 5:29 PM, ClausB said:

If you have already modified the board as above, then cut the bare wire to pin 21 and jumper a new wire from 21 to 24 as below. If you have not yet modified the board, then do not cut the trace between 21 and 24 and do not add the bare wire to pin 21.

 

Hi friend. I did the above circuit exactaly as you sugest. I used a smd 74LS04  and the device works PERFECT with both 2516 and 2716 ones!!
But I removed a HN482732AG-25 from a working RIVER RAID cartridge and did an UV erasing. After the erasing process I did a Blank Test and the software says BLANK CHIP OK! So I burned it in with the MOUSE TRAP NTSC ROM (I am sending it attached this message) and the programming process ran everything ok. When finished, the system checked the file and the eprom

content match the file all ok!
But when installed the eprom in my cartridge, it does NOT WORK !!! 
I tryed several times but it never works!!!!
So I dump the file from the not working chip and try it in the Stella and the dump file works great!!!!
What is wrong????
Why my device works with 2716 but NOT with 2732 ???
Please help me.
Thanks friends!

TESTE MOUSE TRAP.BIN

[ClausB]

The original modification works for the 2732 and the new modification for the 2716. 

 

In your first post you said the 2732 worked and the 2716 did not, so I suggested a mod for the 2716. If you want the board to work with either, then add a switch to pin 21.

Edited August 13, 2020 by ClausB

[pcrock]

10 hours ago, ClausB said:

The original modification works for the 2732 and the new modification for the 2716. 

 

In your first post you said the 2732 worked and the 2716 did not, so I suggested a mod for the 2716. If you want the board to work with either, then add a switch to pin 21.

Thanks for replying. I thinked that would work to both 2732 and 2716 the same circuit. So I will must to include a switch. Very thanks again. 

[pcrock]

I am back to the original modification. 

Connected pin 21 to A11 instead +B and now all working for both 2716 and 2732. 

Don't now the reason why but is good now. 

Special thanks for the help!!!

 

[pcrock]

13 hours ago, ClausB said:

The original modification works for the 2732 and the new modification for the 2716. 

 

In your first post you said the 2732 worked and the 2716 did not, so I suggested a mod for the 2716. If you want the board to work with either, then add a switch to pin 21.

Finally all SOLVED.
I found that ClausB is RIGHT!!!!

 

It happens that some kind of 2716 works fine with the pin 21 connected to A11 but some NOT!!!
I have several brands and kinds of 2716 chips here and tested all with my cart. All of then works good but some chips works fine with pin 21 connected to +B and works fine with pin 21 connected to A11 too but some chips ONLY WORKS if pin 21 is connected to +B 5V!!
So, as sayd ClausB, I will need a switch to correct run any kind of both 2716 and 2732.
I have no words to thank you friend.

[pcrock]

Soldered a Switch at PCB and now it works great using any chip!!
Sorry for the poor pictures.
Thanks for the friends that teach me here!
 

Edited August 15, 2020 by pcrock

[ClausB]

Glad to help.

[pcrock]

What is the reason we need to do this trick to use 27XX in original Atari cartridges???
The originals chips is not a real 27XX ?? How the original pcb does not uses any additional circuit to work but we need to put an inverter to???
If the original chips is not a 27XX, how was it dumped firstly? Were The original rom games modified to work in 27XX ??
 

[ClausB]

The original chips are called mask ROMs. The data are built in at the factory. They can be built with active high chip select lines so they don't need the inverter. In the Atari 2600 the ROM chip select signal is simply A12 from the CPU. When A12 is high then the ROM is active and when it's low the other chips are active. 27xx EPROMs are made with active low chip select inputs, so you need to invert A12 for those. The game code does not have to be changed to put it into an EPROM.

[pcrock]

On 8/23/2020 at 11:09 AM, ClausB said:

The original chips are called mask ROMs. The data are built in at the factory. They can be built with active high chip select lines so they don't need the inverter. In the Atari 2600 the ROM chip select signal is simply A12 from the CPU. When A12 is high then the ROM is active and when it's low the other chips are active. 27xx EPROMs are made with active low chip select inputs, so you need to invert A12 for those. The game code does not have to be changed to put it into an EPROM.

Very very thanks friend for be so patient with me and my asks!!

[areeve]

I have an Atari ROM cartridge that does not work (Thunderground from SEGA). After a cleaning my next step is to check all the contacts and then the ROM chip. So far everything checks out. It has a 2732 EPROM in it, but oddly it has no circuitry to invert the chip select. I have double checked the EPROM using another cartridge with the CS inverted and that worked too. My questions... a) Can I not just tie A12 to ground for the chip select to be active? b) If not then this seems like it could never have worked? The board has notches that fit the case perfectly and I got this cartridge like 20 years ago before there would have been any real reason to counterfeit... any ideas?

 

Thanks in advance for any help.

[Bruce Tomlin]

Most 2K/4K games with mask roms were made with an active-high chip select at the factory as a very minor mask modification. 8K games often had the bank select built in too. It's cheaper to get a slightly custom ROM chip than to add another chip to the board.