[HN Gopher] Towards an HD44780-Based Video Mode
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Towards an HD44780-Based Video Mode
Author : ingve
Score : 108 points
Date : 2021-05-07 15:06 UTC (7 hours ago)
(HTM) web link (github.com)
(TXT) w3m dump (github.com)
| phiiiillll wrote:
| Reminds me of the 1024 color CGA hack
| https://int10h.org/blog/2015/04/cga-in-1024-colors-new-mode-...
| notwedtm wrote:
| Can someone explain this for us mere mortals?
| smiley1437 wrote:
| I think with this project you can control the display at the
| pixel level instead of the character level, like this link in
| the article:
|
| https://m.youtube.com/watch?v=nxFad7Rxw7Q
|
| However that demo is quite old (2013?) so I could be
| misunderstanding something
| st_goliath wrote:
| Long ago, many devices that needed simple text output, like
| super market checkout registers, had simple LCD modules in them
| with e.g. 2 rows with 16 characters each.
|
| Those modules are just bricks with a display on them that you
| can control using a parallel interface. Because of their
| simplicity, they are/were also very popular with micro
| controller hobbyists _long_ before Arduino was a thing.
|
| The HD44780 (and clones) are very widely used controllers on
| those modules. They can be connected in 4 bit or 8 bit parallel
| mode, you can send over characters that it should display
| (using a built in raster font) or some special command
| sequences for e.g. clear the display, set the cursor position,
| ... kind of like a very simple terminal.
|
| The displays with 4 rows instead of 2 typically just had 2 of
| those controllers in them that you needed to interface to. One
| for the bottom 2 rows and one for the top.
|
| Some variants of the controller clones can load a custom font
| lookup table. By breaking a graphical image up into blocks and
| loading those into the font lookup table, you can use the
| device as a very hacky graphics display.
|
| Alternatively, if you rely on semi-documented internals and get
| the timing _just right_ , you can swap out the data while it is
| drawing a character and splice your graphics together that way
| using the built in font. This will also get you a more decent
| refresh rate. Both variants are discussed here.
| smiley1437 wrote:
| Can I play Doom on it?
| MegaDeKay wrote:
| Doom is playable on MiSTer, so assuming this display can be
| used as a generic output device, the answer is yes.
|
| https://twitter.com/misteraddons/status/1283620207978741761?...
| varispeed wrote:
| There is so many clones of these displays, sometimes it's hard to
| get something working, especially to initialise the screen
| consistently. I remember spending so many evenings getting
| display to reset without having to disconnect power physically.
| There is no documentation, or documentation is plainly wrong. If
| you are lucky to get any example code from manufacturer, chances
| are it will not work anyway. But I admit it was fun to "hack"
| those.
| baybal2 wrote:
| Hitachi knew how to make chips. Times change
| thanatos519 wrote:
| I thought I remembered the name from the LCD display on my Apple
| Network Server, which was supported under Linux and gave me a
| mini 'top' on the front of the box... and... I think that was
| enough, thanks.
| transistor-man wrote:
| This is wild. The HD44780 is so incredibly ubiquitous in
| character displays, they are everywhere. Really curious to see
| where this goes.
| neilv wrote:
| Nice! This is a million times cooler than my modest toying with
| these useful little devices.
|
| I have a few of those displays, for a hobby server "front panel"
| project. (3 CrystalFontz with buttons and USB, and an Adafruit
| RGB-backlight one plus USB backpack.) I only got as far as using
| the small set of software-defined characters to do a charts/bars:
|
| https://www.neilvandyke.org/lcdbling/lcdbling-20190121.jpg
|
| https://www.neilvandyke.org/lcdbling/lcdbling-horizontal-bar...
|
| I was planning to use one for my GPU server, and then another for
| a self-contained simple admin console for a home network router
| (no needing SSH/Web to do basic admin functions, nor needing to
| find a sufficiently trustworthy separate device for that).
|
| You can get 5.25" drive bay mounts for some of the CrystalFontz
| ones, including room for D-pad, OK, and Cancel buttons. And
| besides their display and input features, some of them can hook
| into ATX motherboards, and a perform watchdog function, to reboot
| a frozen box.
|
| If you're buying CrystalFontz units that aren't factory-sealed,
| beware that they might've had downstream firmware put on them
| (that's how I got a FireEye one, and a Honeywell one,
| accidentally). A CrystalFontz person told me that the stock
| firmware can only be put on at the factory, but I haven't
| verified this (and I do have a sealed unit from the factory now,
| which I suppose might be cloned).
|
| (Oh, if you're playing with the Adafruit ones, IIRC, the one I
| have seemed to be doing some kind of nonvolatile storage write
| for each color change, at least the way I knew to change the
| color. If that's the case, I don't know whether or how soon a
| write cycle limit on that would be hit.)
| epall wrote:
| This is brilliant! Check out the demo video at
| https://www.youtube.com/watch?v=nxFad7Rxw7Q
| Narishma wrote:
| That's an old demo from 2013.
| dylan604 wrote:
| I kinde of see that screen shaking it's head at the end of it
| going "WTF just happend" like it's waking from some crazy dream
| it just had. That's not what I'm supposed to be used for at
| all!! Sort of like it was just given the choice of a red/blue
| pill
| zwog wrote:
| Amazing. HD47780 displays are not only commercially ubiquitous,
| they were used everywhere when casemodding was still a thing. But
| so far, hardly anyone seems to have thought to exploit the
| possibilities.
| thudson wrote:
| The WEH001602A is pin compatible to the HD44780, with OLED output
| instead of LCD. In 8-bit parallel mode with an FPGA you can
| exceed the recommended clock rate to drive quite a bit of data
| into the displays:
| https://twitter.com/qrs/status/1088240598971310081
| thudson wrote:
| Similar higher-than-rated-bandwidth can be achieved on the
| TRS-80 Model 100, which uses an array of 10 HD44102
| controllers. With an FPGA it is possible to draw full motion
| video on the LCD:
| https://twitter.com/qrs/status/1092410264316653568
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