jamesk Posted January 15, 2011 Share Posted January 15, 2011 I've been working on getting my 7800 setup so I can install an EEPROM (CAT28C65 following this guide here: http://xi6.com/hacks/7800eprom.html I installed a 4 DIP switch so I could install either the original 24 pin ROM (first two switches on) or an EEPROM (last two on). I also socketed the 74LS04 chip (TI SN74LS04N). The original ROM works perfectly. When I have my EEPROM installed the system, cycling the power will display various degrees of failure. Sometimes a black screen with white wavy bars, sometimes an out of sync play field or a play field with various errors in the sprites. Rarely the play field will come up correctly and the game can be played. Looking at Output Enable on my scope the difference between the signal with the ROM vs the EEPROM is obvious. The signal with the ROM behaves and looks the same with each power cycle. With the EEPROM the signal changes with each cycle and during the time that power is on. Sometimes it disappears and other times it never appears. This behavior is visible on both pin 1 and 2 of the 74LS04. So it would seem that there's a problem with the OE signal, but I'm not sure why. Unfortunately I don't have any other EEPROMs or EPROMs on hand to swap out. I think I'll go ahead and find some. Until then if anyone can think of anything to check or do, please let me know. Thanks! Quote Link to comment Share on other sites More sharing options...
GroovyBee Posted January 15, 2011 Share Posted January 15, 2011 Did you double up the BIOS image in the flash part? The NTSC BIOS is 4K and that's an 8K part you are using. Quote Link to comment Share on other sites More sharing options...
jamesk Posted January 15, 2011 Author Share Posted January 15, 2011 Did you double up the BIOS image in the flash part? The NTSC BIOS is 4K and that's an 8K part you are using. Yep.. I set the device offset in my programmer. I also tried just doubling the image file. Quote Link to comment Share on other sites More sharing options...
GroovyBee Posted January 15, 2011 Share Posted January 15, 2011 Can you draw out the schematic of the circuit you've made? Are you pulling the CE of the BIOS chips to the correct state when they are not selected using your DIP switches? Quote Link to comment Share on other sites More sharing options...
jamesk Posted January 16, 2011 Author Share Posted January 16, 2011 (edited) Can you draw out the schematic of the circuit you've made? Are you pulling the CE of the BIOS chips to the correct state when they are not selected using your DIP switches? I didn't touch CE at all since it was not mentioned in the conversion document. According to the 7800 schematic the BIOS has an inverted CE and the 28C65B requires an inverted CE. So there shouldn't be any change there. Edit: I should also mention that 7800 games don't work with the EEPROM at all. Edited January 16, 2011 by jamesk Quote Link to comment Share on other sites More sharing options...
GroovyBee Posted January 16, 2011 Share Posted January 16, 2011 Make sure that WE (pin 27) is pulled high on your flash. The 7800 games need the BIOS to check the signature so that would be expected behaviour at the moment. Quote Link to comment Share on other sites More sharing options...
Bruce Tomlin Posted January 16, 2011 Share Posted January 16, 2011 Make sure to test continuity on EVERY pin. One of the easiest things to do is mess up a trace so that it isn't connected. Quote Link to comment Share on other sites More sharing options...
+5-11under Posted January 16, 2011 Share Posted January 16, 2011 Make sure that WE (pin 27) is pulled high on your flash. The 7800 games need the BIOS to check the signature so that would be expected behaviour at the moment. Also don't leave CE floating. Connect it to ground since you're using OE for control. Quote Link to comment Share on other sites More sharing options...
Lynxman Posted January 16, 2011 Share Posted January 16, 2011 Maybe it is a problem with Pin 1 of the EEPROM. Test again without connect Pin 1 to the socket. I got a problem with the 28C65 (not 7800) and the reason was Pin 1. Quote Link to comment Share on other sites More sharing options...
jamesk Posted January 17, 2011 Author Share Posted January 17, 2011 Make sure that WE (pin 27) is pulled high on your flash. The 7800 games need the BIOS to check the signature so that would be expected behaviour at the moment. Pulled high Make sure to test continuity on EVERY pin. One of the easiest things to do is mess up a trace so that it isn't connected. Continuity checked on every pin. Make sure that WE (pin 27) is pulled high on your flash. The 7800 games need the BIOS to check the signature so that would be expected behaviour at the moment. Also don't leave CE floating. Connect it to ground since you're using OE for control. CE is connected to U11. Pulling it to ground didn't help. Maybe it is a problem with Pin 1 of the EEPROM. Test again without connect Pin 1 to the socket. I got a problem with the 28C65 (not 7800) and the reason was Pin 1. Pin one disconnected without change. Thanks everyone for the suggestions. Quote Link to comment Share on other sites More sharing options...
GroovyBee Posted January 17, 2011 Share Posted January 17, 2011 How about removing the DIL switch(es) from the circuit and directly connecting A15 from Sally through the inverter to the new flash's CE? For a 28 pin device neither W1 or W2 should be connected. If you don't see CE waggling then maybe you've got a dead inverter. Check the inverter's power connections too. Quote Link to comment Share on other sites More sharing options...
jamesk Posted January 17, 2011 Author Share Posted January 17, 2011 How about removing the DIL switch(es) from the circuit and directly connecting A15 from Sally through the inverter to the new flash's CE? For a 28 pin device neither W1 or W2 should be connected. If you don't see CE waggling then maybe you've got a dead inverter. Check the inverter's power connections too. That's a good idea.. I'll give it a shot tonight. I see what you mean about W1 and W2. This is actually really great. I'm learning a lot about the 6502, addressing and other stuff. Quote Link to comment Share on other sites More sharing options...
GroovyBee Posted January 17, 2011 Share Posted January 17, 2011 Are you going to be installing the DevOS or are you doing something else entirely? Quote Link to comment Share on other sites More sharing options...
jamesk Posted January 18, 2011 Author Share Posted January 18, 2011 Are you going to be installing the DevOS or are you doing something else entirely? I was hoping to try out the BIOS with Asteroids on it. Anyway, it seems the EEPROM is going into write mode. After putting the EEPROM in and cycling power a few times the data on the EEPROM starts to change. My EEPROM has a write protection procedure, but unfortunately my programmer can't be made to activate that. So I'm just going to order some EPROMS and start again from there. Quote Link to comment Share on other sites More sharing options...
GroovyBee Posted January 18, 2011 Share Posted January 18, 2011 Anyway, it seems the EEPROM is going into write mode. You must be having activity on WE then. From the schematic I think its connected to A13. Either cut the track and pull the flash side high permanently or pull that leg out of the socket and attach something like a 4k7 pull up to +5v to it and then see what happens. You could also put a scope probe on the flash's BSY/RDY line which will tell you if the flash has entered a programming state. Quote Link to comment Share on other sites More sharing options...
jamesk Posted January 18, 2011 Author Share Posted January 18, 2011 You must be having activity on WE then. From the schematic I think its connected to A13. Either cut the track and pull the flash side high permanently or pull that leg out of the socket and attach something like a 4k7 pull up to +5v to it and then see what happens. You could also put a scope probe on the flash's BSY/RDY line which will tell you if the flash has entered a programming state. YAY! I pulled WE pin 27 with a 2.2k resistor and now it works great with both 7800 and 2600 carts. Thanks for all your help! Quote Link to comment Share on other sites More sharing options...
GroovyBee Posted January 18, 2011 Share Posted January 18, 2011 No probs. Glad to help. Quote Link to comment Share on other sites More sharing options...
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