Javaman Posted July 1, 2015 Share Posted July 1, 2015 Hi everyone, I wired up a little 2k/4k multicart that uses a 74LS04 for a CE hex inverter. It works with the AMD 29F010A-90PC and with some minor wiring changes, the smaller Atmel 28C64-15PCHowever, it will NOT work with the Atmel 29C010A-12PC and I've tried several.Sometimes I get a glimpse of the game screen before it blanks out.An older post http://atariage.com/forums/topic/21851-2732-eeprom-and-problem-with-6-switch-atari/?do=findComment&comment=240804describes a similar problem (though I have a 4 switcher) and he solved it by using a 7406 inverter.Before I take a chance on that inverter does anyone know what might be causing this problem? I'm trying to understand why it would effect the 120ns chip but not the 90 or 150?I really would like to use these chips since I have a few lying around. Many thanks. Quote Link to comment Share on other sites More sharing options...
Javaman Posted July 15, 2015 Author Share Posted July 15, 2015 I fixed my problem. Sounds strange but by disconnecting the ground wire from the ground pin of the eeprom all glitches & flickering disappeared. It had nothing to do with the inverter or speed of the chips. All my Atmel and AMD eeproms work perfectly without a ground wire attached. I even tried this on my handmade 8k multicart based on the pixelspast schematic. That also works better now. Maybe someone has an explanation but I'm glad to have it working. Quote Link to comment Share on other sites More sharing options...
electrotrains Posted July 17, 2015 Share Posted July 17, 2015 Javaman, Are you using a decoupling (0.1uF) capacitor across the +5V/GND of the EEPROMs? I had similar issues when developing a multicart for the atari 8-bit. On a breadboard, I also found that I sometimes also needed an additional 10uF capacitor too. Robin Quote Link to comment Share on other sites More sharing options...
Javaman Posted July 18, 2015 Author Share Posted July 18, 2015 Javaman, Are you using a decoupling (0.1uF) capacitor across the +5V/GND of the EEPROMs? I had similar issues when developing a multicart for the atari 8-bit. On a breadboard, I also found that I sometimes also needed an additional 10uF capacitor too. Robin Yes, I had the 0.1uf cap connected to the 5v & GND pins. Honestly, I tried it both with and without the cap & never noticed a difference. It was only after removing the wire from eeprom GND pin to the GND on the cart that my problem was fixed. I still have the decoupling cap but it's connected to 5V on the eeprom with the other leg directly to ground on the cart. Nothing connected to GND on the eeprom. Quote Link to comment Share on other sites More sharing options...
Shawn Posted July 19, 2015 Share Posted July 19, 2015 pictures? Quote Link to comment Share on other sites More sharing options...
Javaman Posted July 21, 2015 Author Share Posted July 21, 2015 pictures? First one is the bank switching cart based on the PixelsPast schematic. EEPROM on top, GAL20V8B underneath. Got a bit messy tearing it down looking for the original problem. A jungle of wires but amazingly it all fits inside the case. I added extra DIP switches so I could turn on/off the address lines depending on whether there's a F8/F6/F4 GAL in the socket or just running a chip with 2k/4k games. Game selection just uses one DIP. They hold 128k so its (32) 4k games or (16) 8k games, etc. The second board is the first I made. It's a 2k/4k with inverter for chip enable plus an LED just for fun. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.