Tandy VM-1 TRS-80 Monitor : Looking for solutions for Multi Use

[90skidjohnny]

I love all things Tandy. So when I stumbled across an auction for a Green Phosphorus Monitor for less than 35 bucks shipped, I jumped on it. Anywho, it arrived in good albeit, untested shape. I was going to try to test it with My TRS 80 model 1, however that accepts a 5 Pin Din, versus the 8 pin din the monitor supports.

Originally it seems this monitor was mainly purposed to be sold with the Tandy 2000.


Anywho, I found the pinout for the 9 pin din, and its pretty basic, Ground, Video , Horizontal Sync, Vertical Sync, etc ..

My question is, can I (my making my own adapter) Just connect composite to it? Ie, Ground to Ground and Video to Video, and bypass using Horizontal and Vertical sync? As to my understanding composite video just sends all that information over 1 line, wasnt sure if this would be able to be done on this monitor. (or by sending the composite video to both syncs as well)

If anyone has any input or ideas it would be much appreciated!

Thanks and Be safe!

[tipc]

No. A composite (or combined) sync signal has all necessary video information combined in a form so it can be transmitted on 1 line (and ground/return). The monitor's electronics is not designed to break that all down and extract specific information for each of it's stages to be able to produce an intelligible image.

[90skidjohnny]

That is what I was afraid of. hmmm. So pretty much, this thing is really only going to work with a Tandy 2000 I assume? As I have not seen any other computers with this type of connection. I was hoping I could build some sorta of adapter, but, doesn't seem likely at this point. Its such a cool looking monitor too! Bummer.

[90skidjohnny]

Hmmm... Using a LMH1981 IC , i wonder if I could build something? Seems like it could be fun! (yeah im weird)
https://www.ti.com/product/LMH1981

[bladamson]

That monitor is designed to work with a MDA/Hercules card in a PC-compatible. It uses TTL signaling, rather than an analog signal like composite video. It gives you a mono TTL (square wave) video signal and a TTL intensity signal, two bits of video intensity data, for a total of 4 shades of green (or whatever color your phosphor is).

The good news is, MDA cards are really cheap and use a different memory page than CGA/EGA/VGA. So it's possible to install an MDA card in a PC alongside another non-MDA video card and run dual-head, although very little software supports it. FreeDOS has a driver for multihead iirc, but I don't (yet) have an MDA card to test it with so I don't know if it does anything cool or not.

(Note that most MDA cards have a built-in parallel port at 0x3bc irq 7. That's a different IO base address than most multi-io parallel ports, but it uses the same IRQ, so you may have to disable one or the other parallel port to prevent irq conflicts. However, even with the irq entirely disconnected, you can still bit-bang on 0x3bc to control LEDs or relays or whatever, which is kind of a fun use for the otherwise useless parport on the MDA card. Back in college I hooked my coffee maker to a linux box this way to have a timer coffee maker, as components from the electronics lab were free but I was too poor to buy more than a base-model non-timer coffee maker (at least and still afford booze too).)

[Eudimorphodon]

I could be misremembering, but I'm pretty sure the VM-1 isn't MDA/Hercules compatible either. I believe it's set up to run at the same 640x400 resolution as the color Tandy 2000 monitors, which means it probably would not be particularly happy trying to sync with the lower scan frequency of MDA.

[bladamson]

Oh! You are right. I had it confused with the VM-2 (which turns out still wasn't an MDA monitor, so I was wrong either way lolol).

OP: I guess you'll have to get a Tandy 2000. ;3 At least it was only $35, eh?

I wonder what part number the tube is. I could use a new CRT for my Model 4.....

[Eudimorphodon]

I wonder what the pixel clock for that resolution was, if I had one of those monitors I’d love to try driving it with the video dingus project I’m working on...

[bladamson]

I wonder what the pixel clock for that resolution was, if I had one of those monitors I’d love to try driving it with the video dingus project I’m working on...

I have an MDA card that is supposedly capable of a 132 column text mode (!!!), but I don't have an MDA monitor to drive it! XD

But I am fiddling with a GAL circuit that (with the addition of a small R-2R DAC), should convert all of MDA, CGA, and EGA into analog RGB (for input to the ubiquitous and cheap GBS-8200 and output to a VGA monitor). I need to get an EGA card to test it with too, though. But the denizens of Fleabay seem to think that EGA cards are made of precious gems or something. :3

[90skidjohnny]

Thanks for all the info! Bummer tho, Really want a green phosphorus monitor for stuff lol
So, not to beat a dead horse, but still thinking of other options.

I have a TRS-80 Model 1 Monitor as well, which currently isnt working. Been meaning to crack it open and see if i can repair, just havent gotten around to it yet, but I really think it just needs a recap.
Im not sure of the size and such, but in theory, as long as the tube fit, could i swap the tubes? Ive done tube swaps before on color monitors, but wondering if it would work in an application like this. Since basically the TRS monitor is monochrome white.