Curious and weirds Atari 2600 carts.

[pcrock]

I own a Dynacom 8k Kangaroo cart that I think is a curious thing. 

It haves two eproms. What is the reason for that?? Why two ones? 

All ICs numbers (even the logics) were sanded and is impossible to me to know more. 

I have others Kangaaroo carts that uses only one eprom. 

Would be exactlly a half of code on each of them? I yes, why?

 

[pcrock]

Here I have another curious thing. A one chip 8in1 cart. 

All games is 2k ones. 

[pcrock]

" DIGITAL " Game Selection!!!

Another strange to me Dynacom 2 in 1  2K games.
That cart haves an Eprom and one more IC. Both of them were sanded and is impossible to see the chip numbers to identify it!!
Two electrolytic capacitors 1000uF x 10v and 220uF x 10v.
The games are Freeway and Skiing (both from Dynacom).
The game you want to play is selected by touching the metallic contacts (red pointed in the pic I take)
That is a Brazilian cart.

 

 

 

[pcrock]

I would like to ask a question about below cart.
It is a 2 in 1  4K games selected by a switch.
My quest is:
Shouldn't there be an additional inverter circuit for this cartridge to work properly? Where is it ??

 

 

 

[ClausB]

3 hours ago, pcrock said:

I would like to ask a question about below cart.
It is a 2 in 1  4K games selected by a switch.
My quest is:
Shouldn't there be an additional inverter circuit for this cartridge to work properly? Where is it ??

On this cart the 2600's A12 signal connects to the EPROM's /PGM input. The NM27C64Q data sheet says /PGM must be high to read data and pulsed low during programming. I think this cart takes advantage of the EPROM's side effect of disabling its output data when /PGM is low, making it effectively an active high ROM chip select, which the 2600 needs. Clever!

[ClausB]

It's interesting to see the economical construction and design of these Brazilian carts you've shown us in this and other threads. Most have no plated-through holes, no gold plating, no solder mask. They use minimalist circuits in strange and clever ways, often with patched game code. It brings to mind a cottage industry with limited resources but with some smart people.

[alex_79]

Very interesting, thanks for sharing!

That one with the touch switches is really cool! Never seen a 2600 cart like that.

[pcrock]

8 hours ago, ClausB said:

It's interesting to see the economical construction and design of these Brazilian carts you've shown us in this and other threads. Most have no plated-through holes, no gold plating, no solder mask. They use minimalist circuits in strange and clever ways, often with patched game code. It brings to mind a cottage industry with limited resources but with some smart people.

You are absolutely correct!
Everything you just said, accurately describes the Brazilian computer industry in the 70s and 80s! Very few resources, little money and a lot of creativity, intelligence and cleverness!

Here we have a famous saying: "A necessidade é mãe da solução" that means something like "Needing is the mother of the solution!"!

Nowadays we have better resources than in those days, but unfortunately it is expensive when compared to countries like USA, Canada, Japan and part of Europe.

[pcrock]

4 hours ago, alex_79 said:

Very interesting, thanks for sharing!

That one with the touch switches is really cool! Never seen a 2600 cart like that.

Here there were several like this !!

[pcrock]

8 hours ago, ClausB said:

It's interesting to see the economical construction and design of these Brazilian carts you've shown us in this and other threads. Most have no plated-through holes, no gold plating, no solder mask. They use minimalist circuits in strange and clever ways, often with patched game code. It brings to mind a cottage industry with limited resources but with some smart people.

Do you (or some other friend here) understand something to tell me about the Kankaroo cart I placed at the beginning of this post????

[pcrock]

18 hours ago, ClausB said:

On this cart the 2600's A12 signal connects to the EPROM's /PGM input. The NM27C64Q data sheet says /PGM must be high to read data and pulsed low during programming. I think this cart takes advantage of the EPROM's side effect of disabling its output data when /PGM is low, making it effectively an active high ROM chip select, which the 2600 needs. Clever!

Hi friend, thanks again.
Please tell me what you think.
As you can see in the pics I attached, this Board is locked at this time to run two 4K games but it is designed to run till four 4K games. It will works without any inverter with a 27128 ???
The red pointed places in the pics below is the switches to select the games.
 

Edited September 9, 2020 by pcrock

[Danjovic]

On 9/8/2020 at 9:00 PM, pcrock said:

" DIGITAL " Game Selection!!!

Another strange to me Dynacom 2 in 1  2K games.
That cart haves an Eprom and one more IC. Both of them were sanded and is impossible to see the chip numbers to identify it!!
Two electrolytic capacitors 1000uF x 10v and 220uF x 10v.
The games are Freeway and Skiing (both from Dynacom).
The game you want to play is selected by touching the metallic contacts (red pointed in the pic I take)
That is a Brazilian cart.

 

 

 

Hmm that's really odd! Never come across anything similar.

Maybe a RS flip flop with weak pullups, the the finger would force either side to win and thus set either 0 or 1 at one address line of the eprom.

[ClausB]

3 hours ago, pcrock said:

As you can see in the pics I attached, this Board is locked at this time to run two 4K games but it is designed to run till four 4K games. It will works without any inverter with a 27128 ?

Yes, looks like a second switch on those pads would control A13 on a 27128 EPROM. You would have to cut the short trace between the rightmost two pads. But the bigger question is whether /PGM would act the same way on the larger EPROM. If it's a Nat Semi 27C128, then maybe so. Other brands, maybe no.

[alex_79]

Regarding for the "Kangaroo" board, the rom is split into two 4k eproms. The bankswitching logic switches the "chip enable" pins of the 2 eproms so that only the one containing the current bank is enabled.
Some commercial Atari 7800 and atari 5200 games have the rom on separate chips.
And the typical board used for 2600 8k prototypes has two 4k eproms too (here an example).

 

[pcrock]

7 hours ago, alex_79 said:

Regarding for the "Kangaroo" board, the rom is split into two 4k eproms. The bankswitching logic switches the "chip enable" pins of the 2 eproms so that only the one containing the current bank is enabled.
Some commercial Atari 7800 and atari 5200 games have the rom on separate chips.
And the typical board used for 2600 8k prototypes has two 4k eproms too (here an example).

 

Once more Thanks friend!
But  tell me more please. Haves Each of the eproms exactely a half original rom codes ???
If yes, is possible to changes the roms with two 2732 ones that contains a half of Popeye (for example or any original 8K rom) code each one and it will work???

[pcrock]

One More!!!
That is a  4 in 1  (one of it 2k and 3 others 4K). It works perfect.
They use a bigger 27C256 eprom than needed due to be the one they had it in the hands at those days I think.

I attached here the rom dumped from it. The first eprom´s 16K is  all BLANK (FF). How is it possible???
I plan to use that 27C256 in another cart and put a 27C128 here.
My quest is:
What is the reason to use that red pointed resistors connected from pins 6,7,8 to +B ??????????
A 27C128 will work here?

 

27C256_ 4in1 Bowling_Donkey Kong_Kunf Fu_Atlantis.BIN

Edited September 11, 2020 by pcrock

[alex_79]

10 hours ago, pcrock said:

Once more Thanks friend!
But  tell me more please. Haves Each of the eproms exactely a half original rom codes ???
If yes, is possible to changes the roms with two 2732 ones that contains a half of Popeye (for example or any original 8K rom) code each one and it will work???

Yes, each eprom contains half of the rom. As for replacing it with another game, it's no different than for the other boards: you can as long as the game uses the same bankswitching as the old one. If not, it has to be hacked first.
Popeye cannot be converted to work on any of these boards. The bankswitching it uses is very different and more complex than the one used by Atari. (instead of 2 4k banks, there are 8 1k ones that can be mapped in any order in the Atari 4k address space).

 

[alex_79]

6 hours ago, pcrock said:

One More!!!
That is a  4 in 1  (one of it 2k and 3 others 4K). It works perfect.
They use a bigger 27C256 eprom than needed due to be the one they had it in the hands at those days I think.

I attached here the rom dumped from it. The first eprom´s 16K is  all BLANK (FF). How is it possible???
I plan to use that 27C256 in another cart and put a 27C128 here.
My quest is:
What is the reason to use that red pointed resistors connected from pins 6,7,8 to +B ??????????
A 27C128 will work here?

27C256_ 4in1 Bowling_Donkey Kong_Kunf Fu_Atlantis.BIN 32 kB · 0 downloads

The highest address pin (A14 - pin 27) is tied to +5V, so the Atari only "sees" the second half of the eprom. What's in the first half doesn't matter.
Yes, you can put a 27128 in there without modification.
I don't know what's the purpose of those resistors.

 

 

[Danjovic]

Digital Game Selection: By the pinout, most probably be a CD4001

[pcrock]

14 hours ago, alex_79 said:

The highest address pin (A14 - pin 27) is tied to +5V, so the Atari only "sees" the second half of the eprom. What's in the first half doesn't matter.
Yes, you can put a 27128 in there without modification.
I don't know what's the purpose of those resistors.

 

 

I have another 4 i 1 (4K each one game) board absolutely identical to this one but it uses a 27C128 instead 27C256 and it doesn't have the resistors.

Edited September 11, 2020 by pcrock

[pcrock]

9 hours ago, Danjovic said:

Digital Game Selection: By the pinout, most probably be a CD4001

Woowww!! Very Cool idea!!!!

[+batari]

On 9/8/2020 at 9:00 PM, ClausB said:

On this cart the 2600's A12 signal connects to the EPROM's /PGM input. The NM27C64Q data sheet says /PGM must be high to read data and pulsed low during programming. I think this cart takes advantage of the EPROM's side effect of disabling its output data when /PGM is low, making it effectively an active high ROM chip select, which the 2600 needs. Clever!

That is wild. This behavior is not documented in the datasheet, so the only way they could know about it is by experimentation, I think. Funny, I actually have a number of these NM27C64Q EPROMs somewhere. I should dig them out and try this out.

[+batari]

I am curious what those huge electrolytic caps are for. I haven't seen such big caps in any 2600 carts before.

[ClausB]

6 hours ago, batari said:

That is wild. This behavior is not documented in the datasheet, so the only way they could know about it is by experimentation, I think. Funny, I actually have a number of these NM27C64Q EPROMs somewhere. I should dig them out and try this out.

No, it's not explicit in the datasheet but it's implied. In the truth table the /PGM low case is not listed (it's oddly blank in the programming case) but the read case does require /PGM high.

 

Yes, please do experiment and report back.

[pcrock]

Today, another Surprise to me!!!!!
I found one more cart that DOES NOT HAVE any inverter!!!!

 

The words on the CHIP is:

AT&T ´85
QD27128A2
PGM @ 12,5V
INTEL ´83

 

Tha games into the eprom:

 

Frogger (no brand name)
Box By ACTVISION
Crackpots By PROOM
FrostBite By PROOM

 

It appears that exists a lot of 27XX that does not need any inverter to work on ATARI 2600