[Arm-netbook] RGB/TTL interface

[Louis Pearson]

I have been trying to figure out how exactly the RGB interface that the
eoma-68 standard supplies works. Or, in other words, what you would need to
be able to connect it to a screen. The info that I have managed to find
makes me think this would connect directly to a LCD or TTF screen's ribbon
cable. Is there a description of what is provided with this interface
somewhere?

[Luke Kenneth Casson Leighton]

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On Sun, Aug 28, 2016 at 3:42 AM, Louis Pearson

Post by Louis Pearson
I have been trying to figure out how exactly the RGB interface that the
eoma-68 standard supplies works. Or, in other words, what you would need to
be able to connect it to a screen. The info that I have managed to find
makes me think this would connect directly to a LCD or TTF screen's ribbon
cable.

correct. TFT not TTF.

Post by Louis Pearson
Is there a description of what is provided with this interface
somewhere?

RGB/TTL. that's all that's needed to be known. watch out for the
fact that it has a reference voltage VREFTTL.

l.

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[Christopher Havel]

Most TFT screens of relevance here use LVDS, which is entirely different...
TTL as implemented is a parallel 8bit/color scheme IIRC, whereas LVDS is
serial and involves both positive and negative voltages... you'll blow up
the controller in the LCD panel if you hook one to the other.

[Louis Pearson]

So a conversion from TTL to LVDS needs to be done in most cases?

Post by Christopher Havel
Most TFT screens of relevance here use LVDS, which is entirely
different... TTL as implemented is a parallel 8bit/color scheme IIRC,
whereas LVDS is serial and involves both positive and negative voltages...
you'll blow up the controller in the LCD panel if you hook one to the other.
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[Christopher Havel]

Almost all. I can't really help with that -- there should be some sort of
controller or interface chip/circuit there, but that's all I know. I've not
learned much of that sort of stuff yet.

I will say that I once had a TTL LCD panel, 9in diagonal IIRC -- but it was
very strange in a number of other respects in addition to protocol. I'd
gotten it from eBay, and it arrived a bare LCD -- by which I mean that it
was *just* the panel and control circuitry. You could see right through it
-- I was to provide my own backing for it, and backlight as well! Plus the
connector was an odd number of pins -- no key pin, longer on one side than
the other. Weird, weird surface mount thing. Not having any use for it, I
recycled the panel and wrote off the (fortunately fairly minimal) expense.

'Twas a Sharp panel, as I recall. I may still have the datasheet -- I'm
making some adjustments after installing Linux Mint right now on the
machine that would have that document. I'll look when it's done... should
be a half hour or so. Who knows? Maybe it comes with backing and backlight
now... if not, it's still possibly useful if you throw it on an overhead
projector (remember those? :D ) -- I've seen that exact use case in school,
years ago... it's doable. I don't know if it screws with the panel,
though...

[Luke Kenneth Casson Leighton]

On Sun, Aug 28, 2016 at 4:59 PM, Louis Pearson

Post by Louis Pearson
So a conversion from TTL to LVDS needs to be done in most cases?

no - a conversion from RGB/TTL to LVDS (e.g. using a SN75LVDS83b) is
needed on a *specific* case-by-case basis, depending on what LCD you
want to use.

clearly and obviously you would not convert from RGB/TTL to LVDS in
order to connect to a MIPI LCD - you would use an SSD2828 for that.

you would clearly and obviously not convert to LVDS to connect to an eDP panel.

you need to use common sense here.

l.

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[Christopher Havel]

@Luke -- wouldn't most LCDs of the sort we're discussing be LVDS, eg
"donated" from an otherwise-dead laptop...?

True that there are other protocols in use, though...

[Luke Kenneth Casson Leighton]

---
crowd-funded eco-conscious hardware: https://www.crowdsupply.com/eoma68


On Sun, Aug 28, 2016 at 5:41 PM, Christopher Havel

Post by Christopher Havel
@Luke -- wouldn't most LCDs of the sort we're discussing be LVDS, eg
"donated" from an otherwise-dead laptop...?

not necessarily. a modern one witll be eDP. it might be MIPI but
that's unlikely. depending on resolution and age it'll be single,
dual or triple LVDS.

it's literally impossible to know until you either search online or
open up the back (dismantle the laptop) and get the make / model of
the LCD.

l.

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[Christopher Havel]

On Sun, Aug 28, 2016 at 12:53 PM, Luke Kenneth Casson Leighton <

Post by Luke Kenneth Casson Leighton
it's literally impossible to know until you either search online or
open up the back (dismantle the laptop) and get the make / model of
the LCD.

That's true. I'd still argue that, unless it has the shape of a certain
fruit on the other side of the lid ;) the panel inside is gonna be LVDS. I
fully admit to talking out my rear on that one, tho...

[Luke Kenneth Casson Leighton]

---
crowd-funded eco-conscious hardware: https://www.crowdsupply.com/eoma68


On Sun, Aug 28, 2016 at 5:56 PM, Christopher Havel

Post by Christopher Havel
On Sun, Aug 28, 2016 at 12:53 PM, Luke Kenneth Casson Leighton

Post by Luke Kenneth Casson Leighton
it's literally impossible to know until you either search online or
open up the back (dismantle the laptop) and get the make / model of
the LCD.

That's true. I'd still argue that, unless it has the shape of a certain
fruit on the other side of the lid ;) the panel inside is gonna be LVDS. I
fully admit to talking out my rear on that one, tho...

http://support.hp.com/in-en/document/c04913012

eDP

https://www.amazon.com/PROBOOK-Replacement-Screen-Laptop-Matte/dp/B017A5X0Y0

eDP

Post by Christopher Havel
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[Christopher Havel]

Well, then. I have been corrected.

Fun fact: all you need to hook an eDP display up to any computer with a
DisplayPort output -- is a cable that adapts the connectors to each other.
Someone on Hackaday did that a year or two ago. I thought it was neat then
and I still do... don't think I bookmarked it tho.

[Louis Pearson]

Thanks for ask these replies! I'm pretty new to displays do this has been
very informative. For the project in working on, I'll be using a smaller
screen, maybe with a touch screen. Something like this:

http://m.ebay.com/itm/161863547262?_trkparms=aid=222007&algo=SIC.MBE&ao=1&asc=20150831081539&need=62b51881f4054df6a178d0b1ebe1038d&pid=100518&rk=4&rkt=25&sd=262136737363&_trksid=p2349624.c100518.m4111&_mwBanner=1

According to the page it accepts an 8-bit signal. From the looks of it,
this would be able to directly use the RGB/TTL signal.

Another question I have is about SPI based displays. There seems to be a
lot in this size range. Would those be able to display hardware accelerated
video? Is that even a concern with this small of a display?

Post by Christopher Havel
Well, then. I have been corrected.
Fun fact: all you need to hook an eDP display up to any computer with a
DisplayPort output -- is a cable that adapts the connectors to each other.
Someone on Hackaday did that a year or two ago. I thought it was neat then
and I still do... don't think I bookmarked it tho.
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[Christopher Havel]

That's not RGB/TTL... that's parallel 8-bit. Different ball game. RGB/TTL
is either 24-bit (8 bits per color) or 16 bit (6 bits red / 6 bits green /
4 bits blue -- blue is more intense to the human eye so it only *needs*
four bits vs six for another color). The thing you're talking about... that
gets talked to more like a character LCD than anything else. You know the
display on those old HP laser printers you used in grade school? The ones
that could *only* display text, and had a dedicated spot for each
character...? *That's* a character LCD. *That's* the kind of interface
you're looking at here.

Dude, if all you're driving is that kinda thing... use an Arduino. If you
absolutely need Web connectivity (or if you need a little number-crunching
ability but not a lot), use an ESP8266. On that note -- a friend of mine
has found a way to turn off an ESP8266's WiFi side if you don't need it. (Info
here.
<http://www.hackster.io/rayburne/esp8266-turn-off-wifi-reduce-current-big-time-1df8ae>)
If you somehow need something that's more than a fractional-horsepower
driver for it ;) like if you're building some kinda fancy pants Johnny Five
robot... throw a RasPi at it.

Here, this might provide some inspiration --> http://johan.kanflo.com/
the-commadorable-64/
Despite the name, it's a daughterboard for a display like yours, that
integrates an ESP8266 and driver circuitry. You'd have to buy the parts and
solder it together -- and it's almost all surface mount stuff, mind you,
which is a real pain in the tail... but it's worth it from what I can see
here.

EOMA68 is *way* overpowered for any application using that kind of display.
EOMA68 is on the level of a Dell desktop, or at least an older ASUS netbook.

Post by Louis Pearson
Thanks for ask these replies! I'm pretty new to displays do this has been
very informative. For the project in working on, I'll be using a smaller
http://m.ebay.com/itm/161863547262?_trkparms=aid=
222007&algo=SIC.MBE&ao=1&asc=20150831081539&need=
62b51881f4054df6a178d0b1ebe1038d&pid=100518&rk=4&rkt=25&sd=
262136737363&_trksid=p2349624.c100518.m4111&_mwBanner=1
According to the page it accepts an 8-bit signal. From the looks of it,
this would be able to directly use the RGB/TTL signal.
Another question I have is about SPI based displays. There seems to be a
lot in this size range. Would those be able to display hardware accelerated
video? Is that even a concern with this small of a display?

Post by Christopher Havel
Well, then. I have been corrected.
Fun fact: all you need to hook an eDP display up to any computer with a
DisplayPort output -- is a cable that adapts the connectors to each other.
Someone on Hackaday did that a year or two ago. I thought it was neat then
and I still do... don't think I bookmarked it tho.
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[Louis Pearson]

The "project" I'm doing is mostly about learning some new skills, it is a
personal project that I'm doing on the side. It would be a handheld game
console, mostly for GB or NES emulation.

So I guess a Raspberry Pi would be a better target, but... well, I rather
like the idea of EOMA-68. My concept would be similar to the handheld ZEOMA
console, but more reminiscent of the GameBoy. The benefit of using the
EOMA-68 would be the ability to transfer your games between devices very
easily.

Eh, maybe it's not the greatest idea. I could just use a raspberry pi and
it would work mostly the same.

Thanks for the help anyway.

Post by Christopher Havel
That's not RGB/TTL... that's parallel 8-bit. Different ball game. RGB/TTL
is either 24-bit (8 bits per color) or 16 bit (6 bits red / 6 bits green /
4 bits blue -- blue is more intense to the human eye so it only *needs*
four bits vs six for another color). The thing you're talking about... that
gets talked to more like a character LCD than anything else. You know the
display on those old HP laser printers you used in grade school? The ones
that could *only* display text, and had a dedicated spot for each
character...? *That's* a character LCD. *That's* the kind of interface
you're looking at here.
Dude, if all you're driving is that kinda thing... use an Arduino. If you
absolutely need Web connectivity (or if you need a little number-crunching
ability but not a lot), use an ESP8266. On that note -- a friend of mine
has found a way to turn off an ESP8266's WiFi side if you don't need it. (Info
here.
<http://www.hackster.io/rayburne/esp8266-turn-off-wifi-reduce-current-big-time-1df8ae>)
If you somehow need something that's more than a fractional-horsepower
driver for it ;) like if you're building some kinda fancy pants Johnny Five
robot... throw a RasPi at it.
Here, this might provide some inspiration -->
http://johan.kanflo.com/the-commadorable-64/
Despite the name, it's a daughterboard for a display like yours, that
integrates an ESP8266 and driver circuitry. You'd have to buy the parts and
solder it together -- and it's almost all surface mount stuff, mind you,
which is a real pain in the tail... but it's worth it from what I can see
here.
EOMA68 is *way* overpowered for any application using that kind of
display. EOMA68 is on the level of a Dell desktop, or at least an older
ASUS netbook.

Post by Louis Pearson
Thanks for ask these replies! I'm pretty new to displays do this has been
very informative. For the project in working on, I'll be using a smaller
http://m.ebay.com/itm/161863547262?_trkparms=aid=222007&algo=SIC.MBE&ao=1&asc=20150831081539&need=62b51881f4054df6a178d0b1ebe1038d&pid=100518&rk=4&rkt=25&sd=262136737363&_trksid=p2349624.c100518.m4111&_mwBanner=1
According to the page it accepts an 8-bit signal. From the looks of it,
this would be able to directly use the RGB/TTL signal.
Another question I have is about SPI based displays. There seems to be a
lot in this size range. Would those be able to display hardware accelerated
video? Is that even a concern with this small of a display?

Post by Christopher Havel
Well, then. I have been corrected.
Fun fact: all you need to hook an eDP display up to any computer with a
DisplayPort output -- is a cable that adapts the connectors to each other.
Someone on Hackaday did that a year or two ago. I thought it was neat then
and I still do... don't think I bookmarked it tho.
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[Luke Kenneth Casson Leighton]

---
crowd-funded eco-conscious hardware: https://www.crowdsupply.com/eoma68


On Sun, Aug 28, 2016 at 7:59 PM, Louis Pearson

Post by Louis Pearson
The "project" I'm doing is mostly about learning some new skills, it is a
personal project that I'm doing on the side. It would be a handheld game
console, mostly for GB or NES emulation.
So I guess a Raspberry Pi would be a better target,

not really.

Post by Louis Pearson
but... well, I rather
like the idea of EOMA-68. My concept would be similar to the handheld ZEOMA
console, but more reminiscent of the GameBoy. The benefit of using the
EOMA-68 would be the ability to transfer your games between devices very
easily.

exactly. and future upgradeability to faster processors... without
the effort of having to do a total redesign of the base console.

this is why manuel decided to base the hand-held console around EOMA68.

Post by Louis Pearson
Eh, maybe it's not the greatest idea. I could just use a raspberry pi and it
would work mostly the same.

you'll still have exactly the same issues if you use a raspberry pi.
you'll still need to track down a suitable LCD. you'll still have to
work out the interface interoperability.

read these build instructions and tell me if you think it's a good idea:

http://makezine.com/projects/build-raspberry-pi-powered-linux-laptop-that-fits-your-pocket/

l.

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[Luke Kenneth Casson Leighton]

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On Sun, Aug 28, 2016 at 7:01 PM, Louis Pearson

Post by Louis Pearson
Thanks for ask these replies! I'm pretty new to displays do this has been
very informative. For the project in working on, I'll be using a smaller
http://m.ebay.com/itm/161863547262?_trkparms=aid=222007&algo=SIC.MBE&ao=1&asc=20150831081539&need=62b51881f4054df6a178d0b1ebe1038d&pid=100518&rk=4&rkt=25&sd=262136737363&_trksid=p2349624.c100518.m4111&_mwBanner=1
According to the page it accepts an 8-bit signal. From the looks of it, this
would be able to directly use the RGB/TTL signal.

nope - as chris points out, that's a "MCU" style interface (similar
to the old IBM XT bus). 8-bit data/address, 1 line to say "it's
address or data", 1 bit to say "it's read or write" and another for
"clock".

you _could_ use it... you'd have to track down the datasheet for the
controller IC.

basically.... welcome to my world! now you see why the project's
taken 5 years! you've been on this for 2 days and you're tracking
down just *one* of the components - the LCD! now you also have to
find a trusted supplier...

Post by Louis Pearson
Another question I have is about SPI based displays. There seems to be a lot
in this size range.

yes.. because the controller ICs are extremely low-cost.

Post by Louis Pearson
Would those be able to display hardware accelerated
video?

not a snowball in hell's chance. 25mbit/sec *serial* data transfer -
you can do the maths.

Post by Louis Pearson
Is that even a concern with this small of a display?

try to find a video of the Adafruit HX8357D SPI-based LCD, you'll see
that the drawing rate is veeery slow.

l.

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