Displaying external VGA signal on an SE/30s display

[lagomorphonic]

I can't seem to find a single mention of this anywhere, though I've found dozens trying to go the other way. I'd like to gut my SE/30 and use it as a dummy terminal for a PIC24 based computer I'm building. By "gut" I mean I want to use only the case and display (if possible) from the SE/30 and completely remove the internal board. I'll be using "Geoff's VT100 ASCII Terminal" as the heart of it: https://geoffg.net/terminal.html. Basically, it will be a dummy terminal with the aforementioned ASCII Terminal hardware driving the SE/30 display and connected via serial to the PIC24 board. The version of the ASCII Terminal I'll be using has only a VGA output, not a composite. It's a terminal so will only be displaying text. Is it possible to input a VGA signal directly to the SE/30's CRT? Or if not, is it feasible to modify it to do so in a way that doesn't require the SE/30 main board? I also would rather not do anything irreversible to the SE/30 if possible.

Please don't suggest installing terminal software on the OS on the SE/30 and connecting to the PIC24 via RS232/serial connection "instead". I've done that before. That's not what I'm looking to do here.

Thanks!

 

[hauke]

I probably shouldn't lend a hand for such an atrocious deed, but anyway...

VGA has a minimal resolution (and associated timing) of 640 x 480 @ 60 Hz.

Your SE/30's monitor hardware supports a resolution (and associated timing) of 512 x 348 @ 60 Hz.

Naively feeding VGA timing to the poor SE/30 monitor may well end up in a fire, since the HT generation in vintage display hardware is tied to line frequency.

You would have to either teach your implant to produce the macintosh video timing, or replace the monitor hardware.

Or just leave the SE/30 be, and hand it on to somebody who appreciates it.

 

[pizzigri]

Or just leave the SE/30 be, and hand it on to somebody who appreciates it.

as someone that started off getting a Pristine Color Classic to destroy it to build a Takky, and before performing such an atrocity have seen the light and therefore the error of my ways, I could not have said it differently. But, please do not consider this a flame or a judgement - you could still find a fried or just the shell of a SE and then build a “dumb terminal” using suitable internal hardware?

 

[cheesestraws]

This involves both precise timings and high voltages.

If you are not already intimately familiar with working with old CRTs, I would suggest not doing this. Destroying stuff on the AB is the best outcome you can reasonably expect if you just wade into it.

 

[mg.man]

I'd like to gut my SE/30 and use it as a dummy terminal

Um... why not just use MacTerminal?

MacTerminal - Wikipedia

en.wikipedia.org

 

[byates]

Since you don't want to make irreversible changes to your SE/30 you might be able to mod this:

GitHub - dquadros/RPTerm: Serial Terminal Firmware for RP2040 Boards

Serial Terminal Firmware for RP2040 Boards. Contribute to dquadros/RPTerm development by creating an account on GitHub.

github.com

Or check https://hackaday.io/ for ideas.

Implementation and safety concerns are left up to you. Be safe and don't get killed.

 

[zigzagjoe]

I'd be lying if this seemed like the best use of a SE/30 either. That aside, from a technical perspective, VGA input is not technically impossible but it would be annoying, it would require invasive changes to the analog board and/or complicated conversion logic ala Xceed grayscale, and as mentioned risky to both you and the Mac.

A simpler solution would be programming a microcontroller to spit out a B&W signal similar to the original SE/30 motherboard video section. You'd have a tight timing requirement and need fiddly code to get it done, but I suspect it'd be doable with a Pi Pico with its PIO peripherals and ultimately much less risky. You probably could even work from that repro @byates posted, just rip out the VGA code and/or transmogrify it.

Nothing simple, easy, or off the shelf. I echo the "just use macterminal" as the appropriate level of effort, or @cy384's new SSHeven program.

 

[lagomorphonic]

I was looking (hoping) for an MCU based VGA converter or something like that that might already exist. Not really far-fetched considering probably most of the Macs owned on this forum (including mine) are kept alive and relevant by the likes of these "cybernetic" implants (and the modders have even escaped judgement when The Internet says it's the cool thing to do!) @byates thanks for that link. Barring an off the shelf converter, modifying the video terminal source code (PIC32 on the ASCII Terminal) was the next suggestion to myself, but it looks like modifying the RPTerm code might be easier (and just using the RPTerm over the ASCII Term). In any case, I think I like the RP2040 based solution better as I have more experience with them (not to mention a drawer-full of them!).

 

[lagomorphonic]

You would have to either teach your implant to produce the macintosh video timing, or replace the monitor hardware.

Thanks for the notes on timing and helpful suggestions. It looks like that's going to be the plan.