Full writeup here: http://www.glitchwrks.com/2022/06/22/6507-sbc

BillO traded me a blank board for his then-current OMS-02 6507 SBC back in 2011. He was interested in building one of my 8085 SBCs and I just happened to have a spare board for the 8085 SBC rev 2 on hand, at that time. He provided the CPU, ROM, and an ACIA with the bare board. Here's what it looked like when I originally built it up, in 2011:



I recently decided to do some rework on it to fix up a few things about the original build I wasn't satisfied with. Here's its current state:



Most notably, the huge orange Sprague electrolytic has been replaced with something shorter I also had to change the 0.1uF caps around the MAX232: the one I used in 2011 was fine with 0.1uF, but I stole that one for another project at some point, and the replacement didn't like caps that small. I stuck in some 0.33uF radial ceramics I had on hand, which seem to be fine. I also installed a shrouded expansion header with latches (displaced a bypass cap, which is on the back now), and socketed a 74LS138 used for memory decode. The socket is for future hacking. Added a C&K pushbutton with 0.1" lead spacing for reset, just happened to have it in the junk drawer.

I ported GWMON-65 to the 6507 SBC and couldn't get it going. It wouldn't sign on, and debugging was getting me nowhere. I'd sometimes get a few garbage bytes out of the serial port. I was ready to shelve it for a little bit but decided to test some solder-pull Rockwell R6551s I'd scavenged. To my surprise, GWMON-65 came up immediately! I thought about it a while and figured maybe the reset pulse from the unbuffered cap-and-resistor reset circuit was holding the CMOS RCA CDP65C51A in reset longer than the NMOS R6551. Sure enough, that was the problem, something about the speed or shape of the reset pulse caused it to hang in reset longer than the CPU. I hacked in a DS1233 EconoReset:





That fixed it up, and now GWMON-65 works just fine with the CDP65C51A! I'm planning on doing some hacking/expansion on this SBC in the near future, but figured I'd post about it before I started modifying anything.

Nice bit 'o troubleshooting there, glitch. And thanks for sharing the update.

Just one thing. On this forum you're allowed to attach images to your posts... and in fact this is preferable. It's easier than using a third party image hosting site, and the results are more permanent. Finally, there's usually a preview image, which is nicer because a full size image from Imgur or wherever can force folks to do a lot of horizontal scrolling.

-- Jeff

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In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

Nice work. I still have one of these around that I occasionally drag out. I'm going to do your reset mod.

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Bill

I usually cross-post to more than one forum, so I typically use Imgur for picture hosting. That way, I'm not uploading multi-MB images to several forums.



Awesome! The DS1233 bodges in there pretty well.

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http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

I appreciate the sides to the argument, but hosting on Imgur lets me copy/paste the body of the post to other forums -- that way I don't have to deal with often-broken image upload features, upload size limits, number of image limits, etc. which are often poorly configured on other forums. If the load time of the preview image is a big deal, I'll just use one of the smaller thumbnail options in the future.

It's not what many of us prefer, but I think we'd rather have some images than no images!

It is unfortunately true that in the long run every hosted image will disappear - the best one can do is hope that it was saved in the Internet Archive's Wayback Machine.

Quite a few images from my own (older) posts have gone, and I find it quite regrettable.

I've been on some forums that run a plugin or something that grabs remote images and saves a copy on their own servers. If folks feel strongly about it, I'd think that's the way to go! I certainly wouldn't care if forums were doing that with images I was posting publicly.

The other thing hosting on e.g. Imgur does is, it prevents folks from getting some tiny resolution preview that they can't expand unless they're signed up as a member. I hate that, but I'm on at least one forum that still does that with pictures uploaded to their server. I think it makes new folks less likely to benefit from a forum thread they dig up in a search.

I think that's the thing - the conventions and approaches on different forums are different, and here there is a preference for using attachments.

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http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?