My first try at EPROMs
Moderator: Moderators
My first try at EPROMs
So I finally got some time and patients to try this out, here are the details...
I built the EPROM adapter so that I could try replacing ROMs inside my VIC-20. I found the wiring online and wiped out the soldering iron. After a few adapters had been made and some ROMs programed, I pop-ed open the hood and grabbed the character rom after installing the new rom I got a normal screen ( no garbled characters). After pulling it in and out I did not get a good screen, I kept getting a bad screen (see pictures), once in a while I got a good screen but the failure rate is 9/10. If I replace the EPROM with the original ROM I get no issues at all???A little bit of help?
And if your asking why I'm trying to replace the character ROM the answer is I'm not. This is only for testing purposes!
I built the EPROM adapter so that I could try replacing ROMs inside my VIC-20. I found the wiring online and wiped out the soldering iron. After a few adapters had been made and some ROMs programed, I pop-ed open the hood and grabbed the character rom after installing the new rom I got a normal screen ( no garbled characters). After pulling it in and out I did not get a good screen, I kept getting a bad screen (see pictures), once in a while I got a good screen but the failure rate is 9/10. If I replace the EPROM with the original ROM I get no issues at all???A little bit of help?
And if your asking why I'm trying to replace the character ROM the answer is I'm not. This is only for testing purposes!
-Floopy
Re: My first try at EPROMs
The answer is in this thread http://sleepingelephant.com/ipw-web/bul ... 058#p76592 The charcter ROM had to be wired differently than the basic or kernal ROMs do. Apparently because of the way it is accessed by the VIC-1 directly. Also the EPROM apparently has to be faster than 300 ns. I haven't replaced a character ROM myself, It's usually the kernal that goes bad most of the time for some reason.
Norm
Norm
“In religion and politics people’s beliefs and convictions are in almost every case gotten at second-hand, and without examination... whose opinions about them were not worth a brass farthing.”
-Autobiography of Mark Twain
-Autobiography of Mark Twain
Re: My first try at EPROMs
I will try replacing the kernal and see if I get any issues. I'm just testing my adapters, this is only for testing purposes I have no reason to replace my character ROM at all.
-Floopy
- eslapion
- ultimate expander
- Posts: 5458
- Joined: Fri Jun 23, 2006 7:50 pm
- Location: Canada
- Occupation: 8bit addict
Re: My first try at EPROMs
You're not providing any technical details that would allow helping you. The original VIC-20 character generator is a 2332 which uses 2 different independent chip select lines. Definitely the most complicated to replace and it usually requires an EPROM along with a logic gate.Floopy wrote:...I pop-ed open the hood and grabbed the character rom after installing the new rom I got a normal screen ( no garbled characters). After pulling it in and out I did not get a good screen, I kept getting a bad screen (see pictures), once in a while I got a good screen but the failure rate is 9/10. If I replace the EPROM with the original ROM I get no issues at all???A little bit of help?
To top the cake, a C64 CG will not work on the VIC-20 because CS2 is active high on the C64, while it is active low on the VIC-20.
Using the kernal instead of the CG would have made your first experience much easier.And if your asking why I'm trying to replace the character ROM the answer is I'm not. This is only for testing purposes!
Be normal.
Re: My first try at EPROMs
Yea.....eslapion wrote:The original VIC-20 character generator is a 2332 which uses 2 different independent chip select lines. Definitely the most complicated to replace and it usually requires an EPROM along with a logic gate.
To top the cake, a C64 CG will not work on the VIC-20 because CS2 is active high on the C64, while it is active low on the VIC-20.
.
I obviously have no experience in this, but this is why I'm trying.
norm8332 wrote:The answer is in this thread http://sleepingelephant.com/ipw-web/bul ... 058#p76592 The charcter ROM had to be wired differently than the basic or kernal ROMs do. Apparently because of the way it is accessed by the VIC-1 directly. Also the EPROM apparently has to be faster than 300 ns. I haven't replaced a character ROM myself, It's usually the kernal that goes bad most of the time for some reason.
Norm
I tried today and I had no issues at all, I think my ignorance is just the problem here.
-Floopy
Re: My first try at EPROMs
Well this confirms that my adapters work , I may try building something that look nicer later.
-Floopy
- Mike
- Herr VC
- Posts: 4870
- Joined: Wed Dec 01, 2004 1:57 pm
- Location: Munich, Germany
- Occupation: electrical engineer
Re: My first try at EPROMs
Nothing complicated about that. /OE and /CS of a 2732 with an adapter socket do the job, without any extra logic.eslapion wrote:[...] The original VIC-20 character generator is a 2332 which uses 2 different independent chip select lines. Definitely the most complicated to replace and it usually requires an EPROM along with a logic gate. [...]
See the link to the relevant thread norm8332 pointed to in his post above.
- eslapion
- ultimate expander
- Posts: 5458
- Joined: Fri Jun 23, 2006 7:50 pm
- Location: Canada
- Occupation: 8bit addict
Re: My first try at EPROMs
Last time I checked, 2732 EPROMs were as rare as hen's teeth. Anyways, I got confused with the C64 CG which has one /CS active high and another one active low.Mike wrote:Nothing complicated about that. /OE and /CS of a 2732 with an adapter socket do the job, without any extra logic.
You can always use a 27256 or 27512 which are still being made, I guess.
A propos... I just checked Digikey and they now carry the 27C512 in surface mount only. Mouser still carries the DIP version but it's a clear sign this is going the way of the dodo.
Be normal.
- Mike
- Herr VC
- Posts: 4870
- Joined: Wed Dec 01, 2004 1:57 pm
- Location: Munich, Germany
- Occupation: electrical engineer
Re: My first try at EPROMs
eslapion wrote:Last time I checked, 2732 EPROMs were as rare as hen's teeth.
http://sleepingelephant.com/ipw-web/bul ... 48&start=9I got confused with the C64 CG which has one /CS active high and another one active low.
- eslapion
- ultimate expander
- Posts: 5458
- Joined: Fri Jun 23, 2006 7:50 pm
- Location: Canada
- Occupation: 8bit addict
Re: My first try at EPROMs
Yeah, I remember. I must edit that post to specify the CS2 on the C64 CG is active high.
Be normal.
Re: My first try at EPROMs
I've been buying what I think are Chinese clones, like here: https://www.ebay.com/itm/172533017593 They have been working fine (time will tell).eslapion wrote:Last time I checked, 2732 EPROMs were as rare as hen's teeth.
Ebay is literally flooded with these "new" ST EPROMS right now.
Last edited by norm8332 on Sat Nov 11, 2017 3:21 pm, edited 1 time in total.
“In religion and politics people’s beliefs and convictions are in almost every case gotten at second-hand, and without examination... whose opinions about them were not worth a brass farthing.”
-Autobiography of Mark Twain
-Autobiography of Mark Twain
- eslapion
- ultimate expander
- Posts: 5458
- Joined: Fri Jun 23, 2006 7:50 pm
- Location: Canada
- Occupation: 8bit addict
Re: My first try at EPROMs
Yeah, the datecode (1035) is quite interesting. There is no way SGS-Thomson was making more 2732 EPROMs in late 2010.norm8332 wrote:Ebay is literally flooded with these "new" ST EPROMS right now.
Also look at the size of the die. I have real 2732s here and they are 4 times bigger.
Be normal.
Re: My first try at EPROMs
What would you use 2K eproms for?norm8332 wrote:I've been buying what I think are Chinese clones, like here: https://www.ebay.com/itm/172533017593 They have been working fine (time will tell).eslapion wrote:Last time I checked, 2732 EPROMs were as rare as hen's teeth.
Ebay is literally flooded with these "new" ST EPROMS right now.
-Floopy
- Mike
- Herr VC
- Posts: 4870
- Joined: Wed Dec 01, 2004 1:57 pm
- Location: Munich, Germany
- Occupation: electrical engineer
Re: My first try at EPROMs
2732 EPROMs hold 32 kbit ^= 4 KB. That's entirely sufficient to store a small homebrew on cartridge, like I did with TRON Light Cycles.Floopy wrote:What would you use 2K eproms for?
Re: My first try at EPROMs
I was dividing by 16
I'm only making myself look even more ridiculous.
I'm only making myself look even more ridiculous.
-Floopy