HELP! Need advice on why these carts do not work (Homebrews)

[Cassidy Nolen]

Ok,

 

I am getting all ready for Philly this year. I thought I would really be ahead of the game. Got all my eproms, burned the new Polo binary onto them (thanks to Chris Tumber's great intro), and bought all new boards (Joe Grand's boards). I checked all my eproms, and they all tested fine.....until about number 15. I turned the unit off, and waited a minute, then they tested fine. I did not think anything about it. Maybe a bad connection.......

 

 

So I went ahead and assembled all the boards, chips and cartridges. I had my wife check them all out on the system. The first 13-14 were fine, but then they started acting up. It did not matter what game you put in (any one of the carts, even the ones that just worked, ), they all have "garbage" on the screen, and the intro is all messed up. I switched 2600's, and they were fine, for about 5-10 tries. After that, they started acting up again. The Polo game is a 2K image, and the 2732 is a 4K chip. The intro is a 2K intro, and once you hit reset, it always takes you to the game. The game is fine, its just the intro.

 

Here's my question: Has anyone ever seen this? I did not use a capacitor on these carts, could that be it? I can't imagine that is it, but maybe? If you leave the system off for a few minutes, the games work fine. HELP!

 

I am completely confused.....

 

Cassidy

[Thomas Jentzsch]

Hm, just a quick guess:

 

Maybe the initialization code of the intro misses something (e.g. clearing the BCD flag register).

 

Is the binary or code of the intro available somewhere? Probably the first about 100 bytes would be sufficient too.

[Cassidy Nolen]

Would that make it a truly "random" problem, depending on the state of the processor when it fired up? It seems to be a warm "start" condition; maybe like a capacitor is charging up, and then causing it to happen after so many cycles. If you let the system "cool" down (off for 3 or more minutes), it does not do it for about 5 on/offs, no matter what cartridge it is.

 

Thanks for the idea. Would you mind if I forwarded you the bin? I would really appreciate the help.

 

Cassidy

[CPUWIZ]

You do need the filter capacitor, I am pretty sure about that.

[Thomas Jentzsch]

Would you mind if I forwarded you the bin?  I would really appreciate the help.

Thanks, I already got the source from Chris.

 

I think the problem is very obvious: There is NO! startup code at all.

 

Normally the first thing a 2600 games has to do, is to clear the whole zeropage and the BCD flag and to initialize the stack pointer. This is no big deal, I think Chris can add the setup code in a minute.

 

I really wonder how the games did work at all.

 

Looks like most of the registers and flags of a "cold" 2600 are in an acceptable state.

[Cassidy Nolen]

You guys are amazing. Thomas, thank you. Its people like you that make it worth being a collector. I truly appreciate your time and expertise on this matter. I also want to thank Chris again for even talking to me about it, let alone working on an intro at all! Simply amazing what you all can do with the 2600. Thanks.

 

I really wish I had not made 30 of them already. Might try and fix up some setup where I do not have to unsolder/solder 1400 connections.

 

Thanks for the tip on the caps, too. I had never heard of that before. Hozer did not have them on his setup, and even on the bankswitching carts I have built, there are no caps shown. All the Polo's out there that I made do not have them. Wild.

 

Not being lazy, just did not know!

 

Thanks guys. Amazing it worked, you are right. Now to drop Chris an email.

 

Cassidy

[Christopher Tumber]

I *think* the problem is that I forgot to set the stack pointer so if the state of the stack is maintained for a short time even once powered down (ie: until capacitors discharge) then eventually the stack may work it's way down into and overwrite the wrong RAM locations....

 

Crap! Crap! Crap!

 

 

Chris...