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VGA->Arduino->Mac Portable LCD

LaPorta

Well-known member
Wait, so inputting to the Portable LCD an external video signal? Goal to create a stealth new machine in the portable?
 

Trash80toHP_Mini

NIGHT STALKER
You caught me! LOL! ;) Let's call it a Steampunk Luggable for the moment. NiCad developments pushed back by a couple of years in this scenario. Been in high rev. hypo-manic mode, not Psychotic thanks to a fabulous meds cocktail. 🤪

But insane images have been dancing around my head when falling asleep and waking up. Lets just say I've moved on from the IIsi, my favorite hack victim. Point here is to insert Arduino as a Black Box for what Apple would have easily done in a rudimentary ASIC or a simple silicon implementation. Can't help myself, been trying my best to derail another reverse engineering project.
 

LaPorta

Well-known member
I think this is pretty cool. If someone can figure this out, maybe we also have a chance at making the ever-elusive Portable video-out port work as well!
 

Trash80toHP_Mini

NIGHT STALKER
HEH! ;) A bit ahead of Apple's Steampunk development curve on that, 832x624 @16bit is already in the spec for either/or switching machine states. Second display requires one of my VidCards for 8bit pixellation at that resolution.
 
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LaPorta

Well-known member
It most definitely is in the Macintosh Family Hardware book, I have seen it myself. Of course, my library is in boxes while I am waiting to move....but it definitely is in there.
 

Trash80toHP_Mini

NIGHT STALKER
LOL! My Library is boxed up too, but .PDF backups are available . . . and handier for this kind of thing:

Portable_III-LCD-p1.JPG
Portable_III-LCD-p2.JPG
But I've seen a lot more detailed version somewhere? Download the third edition, not available on HDD ATM.
 

LaPorta

Well-known member
That's the one that I have, your photo above. I actually have the second edition book on the way to my house from eBay....didn't know there was a 3rd.
 

Trash80toHP_Mini

NIGHT STALKER
Just took shots of parts for this Steampunk monstrosity. This'll be my first time in AI for quite some time. But that's for another thread. After you guess the donor board (DOA of course) for the new AltVersePortable build we'll drop anything off topic.

Gotta get the BLACK BOX Vid-uino or eq. substitute worked out here. KBD/NumPad-uino ADB converter is at least half done in another old thread. Long live the rodent! ;)
 
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Trash80toHP_Mini

NIGHT STALKER
That's for its own DevThread, this one is for the Arduino boffins to chime in. Whatcha think gang, is there any way to get this done? I wonder if the mfr's specs on this LCD are waybacked?
 
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Trash80toHP_Mini

NIGHT STALKER
OK. mulled it over a bit and the circuit above is way overkill for the Portable's LCD. RGB can be tied together at one input. The 640x400 60Hz feed will be set to single bit in the Monitors Control Panel.

So each screen redraw gets fed pixel dots sequentially via Analog to Digital conversion into a register or something?
When closing bell for the raster input goes off, the whole shebang gets converted in the Arduino?
That content then heads to Arduino output in 8-bit input form?
Somethingorother receiving input from that side then drives the Portable LCD?

No clue here, obviously. How about a little help or at least some hints from you SBC wranglers?
 

Gorgonops

Moderator
Staff member
Crazy notion of the day: Can this cute little puppy be trained to run in reverse?

To cut to the chase, no. It would be easier to give a precise answer if we had the datasheet for the Portable's LCD, but most of those ancient monochrome LCDs don't use timing anything like a CRT. (This was alluded to in the other thread you linked to this one. Some of these LCDs aren't even all a single plane, they have separate refresh zones for the top and the bottom half of the screen that operate simultaneously, etc.) If you want to try to convert a conventional raster and display it on this thing you're pretty much going to have to capture a full frame at a time on the "in" side and read it out in the LCD's format on the other. Which means your converter is going to require a framebuffer large enough to hold the whole thing, not just a rolling line buffer or other shortcut. Even if it were fast enough to do the capturing part (which would definitely be a stretch) an Arduino's AVR328 has 2K of working RAM, that's not going to cut it.

In principle something leagues more powerful could do it, the RGB2HDMI pulls a roughly similar feat using a Raspberry Pi Zero with a little bit of help, although it must be said that the Raspberry Pi's output side has significant hardware assist *and* the pixel clocks that the RGB2HDMI can officially handle are all significantly lower than VGA. I don't know if any modern SoC's LCD drivers could be convinced to interface with the Portable's LCD, my gut feeling is "probably not", but a datasheet would help *a lot*.
 

Trash80toHP_Mini

NIGHT STALKER
Heh, damn straight. I'll be looking for one, I know there's more and better info I have seen but haven't located. It looks like the panel has quite a few zones to me, but you know how much I don't know.

Interesting that RPi might be a better fit, LOL! We'll see. It's looking like adding the pinout for the PDS for silicon on the board of the LCIII to do the frame buffer grabbing ATM, Dunno, but it's fun to crash and burn, learn a lot that way. ;)
 

Trash80toHP_Mini

NIGHT STALKER
Wondering, if we can grab a full screen buffer shot off the board before it's streamed to RAMDAC, will that be a lot easier to chunk for LCD controller fitment?
 
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