[Arm-netbook] Testing: GPIO

[Richard Wilbur]

On Thu, Mar 1, 2018 at 2:54 PM, Christopher Havel <laserhawk64 at gmail.com> wrote:
> Oh LOL.
>
> VGA is analog, and has six wires for color (red signal, red ground, ditto
> each for blue and green). It's not /exactly/ serial (serial as I understand
> it is inherently digital, which VGA is *ahem* very much not) but the
> paradigm sort of fits. RGBTTL is parallel. You have one wire per bit of
> color. So that's 18 wires. Plus your sync lines... which may or may not
> match VGA signal standards, I'm not sure.
>
> If you actually manage to figure out how to get that hooked up correclty,
> let me know ;)
>
> (Hint, it's doable, but you need additional components. There's a cheap
> way, and there's an easy way, and they are two *very* different ways...)

Looking at the micro-desktop schematic it seems Luke has this issue
well in hand.  Christopher have you seen the micro-desktop schematic?
The VGA conversion is on page 3.

Luke, have you tested the D/A circuit on the micro-desktop board?
Only thing I would worry about is the hold time on the data lines.  If
the A20 sets up the data quickly (relative to the pixel time) and
holds it until the next setup, we should be in good shape.

> Much easier suggestion: get a small LCD. *ANY* small LCD. Like a five or
> seven inch display at the largest. Raw panel, no driver board. Get the
> datasheet and a compatible connector. (If you source from eBay this is very
> easy; those are almost all commodity displays with available datasheets.)
> If it's a SMALL DISPLAY it *will* be RGBTTL, 90%+ of the time (I've seen
> one exception to this ever and it was in an off-brand portable DVD player).
> Wire it up. Wire it to the card connector. Add power. If you get a screen
> that works, you've done it right.

I think this is why Luke put the display signals on the EOMA68
standard in the RGBTTL format--to simplify the job of connecting to
LCD's.  (I'm thinking of the laptop, tablet, gaming console, phone,
etc.)