Similar forum for other retro computers?

[James Harland]

Hi everyone,

I really love this Google group for the active and beginner-friendly community, and am very grateful for all the advice I have got about my RC-2014.

I am also working on getting a couple of Epson HX-20s working to a satisfactory degree. I am in touch with an HX-20 expert, but I feel that my beginner-level questions are kind of annoying him. 

So I wonder if there is a similar community to this one where I can ask such questions about the HX-20 or other retro computers?

Thanks everyone,

James

[Ed Silky]

For Heath ET-3400 (Microprocessor Trainer) and other 6800/6802 'stuff' I've had good experiences with: https://groups.io/g/ET-3400

-Ed 

[Steve Cousins]

https://groups.google.com/g/retro-comp

This was set up a few years ago to avoid the rc2014 group getting too broad, allowing it to focus on rc2014 and not all the other things that were beginning to complicate it. The retro-comp group is a suitable place to ask/discuss any retro computer or vintage computer issues.

[James Harland]

Thanks Ed, Steve, and Harry who responded privately. I've put my project notes up on retro-comp and they've been accepted by the moderator. If I get either of my HX-20s working enough to be able to start looking into 6800 machine code again, then I'll check out the ET-3400 forum too. I do have two Soviet microtrainers, but for different architectures (AM2900 and Intel 8080).

[Ed Silky]

Very good. I saw your post on Retro-Comp. When you get your HX-20s running you can dip into 6800 assembly, since the Hitachi 6309 is compatible. At that point you might find the folks in the ET-3400 group helpful.

-Ed

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[Alan Cox]

6809/6309 isn't compatible so much as has an assembly mode that mostly converts.

Very different to say running 8080 code on rcbus Z80 machines where it's the same binary and almost exact documented behaviours

Alan

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[James Harland]

I think the HX-20 has the Hitachi 6301, so I guess that's suppoed to be 6801 compatible? I've just run the first routine of Leventhal's 6800 book, and it produced the right result. Which yes means by the way that I have got my 'new' HX-20 working after cleaning the keyboard.

Yes, the chips say C6301CB on them. Wikipedia links the 6301 to the Motorola 6809 though so I'm confused.

[Alan Cox]

On Fri, 14 Nov 2025 at 16:38, James Harland <harla...@gmail.com> wrote:

I think the HX-20 has the Hitachi 6301, so I guess that's suppoed to be 6801 compatible? I've just run the first routine of Leventhal's 6800 book, and it produced the right result. Which yes means by the way that I have got my 'new' HX-20 working after cleaning the keyboard.

Yes, the chips say C6301CB on them. Wikipedia links the 6301 to the Motorola 6809 though so I'm confused.

6800 is the original instruction set

6801/6803 are back binary compatible and add instructions. Some are added to fix 6800 flaws others to add 16bit ops

6301/6303 add some more Hitachi only ones and pipelined the original ones so it's faster

68HC11 is back compatible with 6801/3 but not 6301/3, although it does take from 6301/3 but not in a compatible fashion

6809 is a totally unrelated Motorola processor line. There are some assembler level tools for porting 6800 code to it. It does not run 6800 code.

6309 is the Hitachi clone of the 6809 and owing to a bit of a fight with Motorola over the 6803/6303 situation where Hitachi improved on the chip and got all the business, the 6309 extensions were secret and locked away but were later unlocked.

Compare with Zilog where Hitachi did a soup up job on the Z80 and instead of getting into the lawsuits Zilog licensed the Hitachi 64180 back, improved it more and called it the Z180.

Alan

[James Harland]

Great thanks for clearing that up! I think you have the expertise to be able to fix the incorrect link on the HX-20 Wikipedia page (from Hitachi 6301 to Motorola 6809). That's been there for a long time - I see it was there in my notes from 6 years ago, and it confused me back then too.

[Ed Silky]

Very good on getting your HX-20 running James! (one of them anyway)

Hi Alan, thanks for that info. I have an ET-3400, so a 6800. I primarily have Z80 stuff (for my retro work), as I worked as a HW/SW engineer for a company that made Z80/Z180/Z280 based systems (TRIAD Systems in Sunnyvale/Livermore, CA). We worked pretty closely with a group of Zilog engineers, as we did a lot with their chips. One of my projects while working there was designing a Z80 ICE. TRIAD produced it for our in-house use (for HW and our team of SW developers), and a couple went to Zilog (on Bubb Rd in Sunnyvale). I still have one of them and use it to troubleshoot my projects.

-Ed

[Ed Silky]

I can do a separate post for my ICE (ZED = Z80 Emulator and Debugger) if anyone is interested. I can post the schematic, though it uses a few PALs that, unfortunately, I don't still have the listings for. I can also describe the operations that it provides, as a lot of input went into it from both hardware and software engineers.

-Ed

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[Greg Holdren]

 That would be interesting to hear about for sure. Probably on retro-comp though.

Greg