Duodyne Z80 board - Values of xtals at U2 and U3, jumper config

[MxArgent]

So, I've got my backplane and Z80 PCBs on the way! Gonna be a while before I get to the latter, but I'm already trying to get my notes together. I've noticed that neither the schematics nor the CSV/HTML BOMs for the duodyne's Z80 board specify a frequency for the CPU or UART crystals. Gut instinct says the CPU clock should probably just be appropriate for the Z80 I source, and the UART should just be the usual 1.8432MHz, but I'd like to verify before I commit to anything. Is that correct?

Also, does anyone have a photo of a working, properly jumpered board I can reference when I'm ready to build mine? Thanks!

[Dave White]

I have a Z80 PEC10 overclocked with a 12MHz oscillator. The Oscillator on my UART board is 1.8432MHz. 

Which board do you want the photo of, the CPU or the UART? I had most trouble with the memory boards. It took a bit of back and forth with Andrew Lynch to get the correct jumper settings. I built mine very early on, so the Github documentation may be better now.

[MxArgent]

Ooh, documentation on the ROMRAM would be much appreciated then. Anything I should be wary of building that one?

A friend pointed out that there's some build photos that should still be accurate in the "Initial Build and Test" directory, which I missed. That's helped narrow things down for me a fair deal, but the more details I can get ahead of time the better!

[Dave White]

I looked back through my early e-mails with Andrew, and it looks like there was an error in the Github documentation for the jumpers. I followed the online settings and couldn't get my system to boot. After working with Andrew, he recognized the documentation error and fixed it. The the online docs should be good now. I'll take some photos of my boards tomorrow and post them up for you so you can see the jumpers that I'm using and that are working for me.

From memory (it was back in 2022 when I built this), I had no other problems with the build; the memory jumpers were the only issue. It's a great little system.

[MxArgent]

That's good to know! I'm excited to get to work. I'll have a fully built backplane soon, but due to a payroll error it's gonna be a few weeks until I can get to the Z80 board. Do have the PCBs on the way, though! Reminds me, I need to source PCBs for a ROMRAM board, too. Should probably ask around and see if anyone has one spare I can buy before I hit up JLCPCB again.

[Andrew Lynch]

Hi

Regarding the CPU clock, I'd start with something conservative like 4 MHz and increase to the max without overclocking.  10 MHz seems to work well for me although people have gotten it to go much faster.  It's a balance between processing speed versus how fast you can push the peripherals across the bus.

Regarding the UART clock, that's independent from the CPU so you can use whatever speed you want.  However, ROMWBW assumes 7.3728 MHz by default.  You can use other frequencies, but you'll need to set the configuration in ROMWBW to match.

Both the Z80 DMA and RAMROM boards have gotten updates and respins so are improved from the initial versions.  If you find any anomalies, please post so I can update the GitHub page.

GitHub - lynchaj/duodyne: Duodyne is a hobbyist retrocomputer system designed to run ROMWBW. It is comprised of modules on a system bus

Obviously, you are free to post and discuss anywhere you'd like.  However, I suggest using the duodyne groups.io page since everyone there is a duodyne owner/builder.

duo...@groups.io | Home

I haven't been as active as I want recently due to other things in life, however, I am still interested and willing to help where I can.

The base system seems to work well, and I am a big fan of the 4-slot backplane with Z80 DMA, RAMROM, Multi-IO, Disk-IO (or Zilog Peripherals) combo.  It has a lot of general-purpose IO and storage options in a nice relatively compact system.

Of course, the secret sauce is ROMWBW which makes it all possible so kudos to Wayne for all his hard work.

There are still many open possibilities and avenues left to explore so don't let what's come before limiting your ideas.

Have a great day! Thanks, Andrew Lynch

Merovingian: Choice is an illusion created between those with power and those without.

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[Andrew Lynch]

Hi

I rechecked the groups.io admin settings and it seems to allow attachments, so I am not sure what is happening.  Some of the older messages do have attachments.  Any suggestions as to what is not working?

Groups.io limits attachment size to 15 MB so maybe that's the issue?  I don't know.  Maybe try sending a small attachment and see if that goes through.

An alternative would be to post the image on the Github in the "duodyne/!Initial Build and Test/" folder with the other photos and post a link

What I've done is order my own PCBs using the Gerbers and send the extras out to anyone who asks.  There is no point in letting the extra PCBs pile up someplace collecting dust.  I'd rather send them to someone who might use them.

Compared to the other methods I've tried, I think posting the Gerbers and letting people order their own seems to work the best.  It eliminates all the messy money handling and customs issues.  Also, not having to keep inventory on hand which is a hassle.

I am attaching a tiny picture of a Z80 CPU to this message as a test of file attachments.  Please let me know if you can see it.

Thanks!  Andrew Lynch

Merovingian: Choice is an illusion created between those with power and those without.

On Tuesday, July 8, 2025 at 09:26:12 PM EDT, Dave White <mrgcm...@gmail.com> wrote:

For some reason it's not letting me post images. If you contact me at my "junk" e-mail "mrgcms2001 at yahoo  com" I can e-mail you the images if you still need them. Also, what country are you in? If you're in the US, I have a bunch of spare PCBs, including the Z80, 6502 and 6809 CPU cards.

https://groups.google.com/d/msgid/retro-comp/4438781f-61b1-4a58-a793-52a24b8856b0n%40googlegroups.com

.

[Andrew Lynch]

Hi Dave

Yeah, that image file attachment works fine!  Thanks!  Andrew Lynch

Merovingian: Choice is an illusion created between those with power and those without.

On Tuesday, July 8, 2025 at 09:25:28 PM EDT, Dave White <mrgcm...@gmail.com> wrote:

RAM overview - 2 x 512KB with battery backup

On Monday, July 7, 2025 at 7:30:54 AM UTC-5 lyn...@yahoo.com wrote:

https://groups.google.com/d/msgid/retro-comp/6094bfb4-4381-4d3f-af72-a1d809300fb1n%40googlegroups.com

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[Dave White]

Well, I'm an idiot. I was confusing Andrew's Nhyodyne with the Duodyne. I have the Nhyodyne - ignore everything I said above!

On Monday, July 7, 2025 at 7:30:54 AM UTC-5 lyn...@yahoo.com wrote:

[Dave White]

Thanks for confirming Andrew. But in fact I misread the initial post and though the OP was referring to the Nhyodyne - it was only after posting the photos that I realized he was referring to the Duodyne - I'll put it down to a senior moment!

[Andrew Lynch]

Hi Dave

Not a problem.  duodyne derives much of its design from consolidation of Nhyodyne boards so there are a lot of commonalities.

The idea being to make a complete, robust system without an excessive number of boards.  Also, I find the larger format easier to work with.

Thanks!  Andrew Lynch

Merovingian: Choice is an illusion created between those with power and those without.

https://groups.google.com/d/msgid/retro-comp/3cde36ce-e6c7-4f87-98df-68f4dc087b9bn%40googlegroups.com

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[MxArgent]

Oh, I was thinking of a Nhyodyne build before I moved up to the Duodyne. Either would have been a suitable follow up to my SBC V2 build from a few years ago, but I think the Duodyne embodies what I'd like in a multi-year project a little better.

I've completed the backplane! I'm giving it a little more time before I apply power and take test measurements, though it's had plenty of time to dry. I'm no stranger to marathon soldering sessions from my two builds of the N8VEM S100 backplane, but it was a bit harder to pull things off with my work occupying more of my time these days! Next stop's the Processor.Z80 board - This next paycheck is looking pretty good, so i might be able to get both the base PCB and rollup/IC orders in one go. I already have all the PLCC chips including a 10MHz Z80 and a pair of  Z84C1008VEC, though I do want to see if  Z84C1008VEG are still in stock by the time I'm ready to hit up Mouser for ICs. After that, I need to source my RAMROM PCBs - I might just hit up JLC for this again, though I kind of want to ask around on the groups.io list to see if anyone has spares. If I do run my own boards, I could sell off the extras as a three-board combo at VCF Midwest to recoup some of the costs.

Speaking of, my goal right now is to have the machine through phase 1 of the build (backplane/processor/ramrom) in time for exhibition at VCFMW alongside my S100computers stack. I'm also interested in >10MHz operation and have a higher rated Z80 on the way, but that's all for later.