A LCD TFT display and a Propeller. Help and comments needed...

grasshopper

I was instructed to implement a LCD TFT display on my next design and want to use the propeller. I am questioning the memory and the speed of the prop if it would be able to drive a 800x480 resolution monitor?

I was thinking, and; perhaps 3 serial to parallel ICs for the RGB data lines would help. It could free up some i/o on the prop since the display requires 24, 8 per RGB.

Also i searched the forums and was unable to find a driver or any other information that was promising. Any ideas or comments?

data sheet is here

www.apollodisplays.com/pdf/T-55290D050J-LW-A-AAN_071120_Eng.pdf Its a PDF

StefanL38

hello Grashopper,

does it really have to be THIS Display ?
Does it really have to be a Display withh RGB input?

Who wants to use RGB nowadays?

In the library there are drivers for VGA-output.
There are drivers up to 1024x768 pixels in textmode

If i saw it right in the datsheet the DataClock has to be VERY fast 30 MHz !
One assembler-command needs 4 clockcycles this is only 20MHz

Maybe it is possible to to it slower but i don't know what lower speed means to the screen refreshing rate (complete pictures per second)

best regards

Stefan

OwenS

That display has a dot clock of 30Mhz. While you may be able to drive it slower, the display will start flickering and loosing it's picture at lower speeds. That display is quite a bit outside the capabilities of the Propeller alone

grasshopper

No it does not have to be that display in particular but it has to be similar. I need around a 5x5 inch display that is thin and cheap. Cant the prop run at 100Mhz?

grasshopper

What about this one? it says VGA mode, will this work better?

media.digikey.com/pdf/Data%20Sheets/Optrex%20PDFs/T-51380L050J-FW-P-AB%20Spec.pdf

I think 6 mhz is all it is wanting...

Timmoore

This MAY work but I haven't tried it. Start with a vga driver, connect the vga rgb to 6 of the lcd rgb (probably MSB 2 bits of each), and ground the other rgb pins. Connect v/h sync to lcd h/h sync. Modify vga driver to use a counter for dot clk, getting the phase of the clk to the vga output may be difficult. Not sure about dena, you might be able to drive from software or you might have to modify one of the v/s sync to generate it, or use external hardware to generate it from v/s sync.
You will also need to reduce resolution there isn't the memory for 800x480 even at the reduced color depth.
You probably also should choose the prop crystal so the counter can generate a sensible dclk without jitter e.g. a 4Mhz crystal will run the prop at 64Mhz, divided by 2 gives you a clean 32Mhz dclk. Though the question is then whether the prop could run vga at that speed. You could try 5Mhz / 2 for 40Mhz or 10Mhz / 4 gives also gives 40

Sapieha

Hi grasshopper

Thanks for link.
It is fuly VGA compatible

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Nothing is impossible, there are only different degrees of difficulty.
For every stuipid question there is atleast one inteligent awnser
If you dont ask you wont know

Sapieha

RinksCustoms

I've driven my DIP40 prop to 100MHz without side effects, much faster than that & you'll start loosing things... Around 120MHz the outputs began to get random, this could be because of the breadboard or noise in the power side ($40 PSU from an old PC)

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E³ = Thought

http://folding.stanford.edu/·- Donating some CPU/GPU downtime just might lead to a cure for cancer! My team stats.

Post Edited (RinksCustoms) : 9/13/2008 9:33:13 PM GMT

grasshopper

Sapieha said...
Hi grasshopper

Thanks for link.
It is fuly VGA compatible

So i translate this to "It will work". ill order up a few and make some boards. If it works out perhaps i can give away the remaining leftover prototypes.

Thanks so far but stay tuned, , ,

Sapieha

Hi grasshopper.

If I can see corectly it has one mode RGB+H+V sync in.
and one mode RGB+Composite sync in

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Nothing is impossible, there are only different degrees of difficulty.
For every stuipid question there is atleast one inteligent awnser
If you dont ask you wont know

Sapieha

evanh

Interesting, that display is 3.3 volt.

Have a read of my comments here. Then talk to Baggers about timings that might be achievable.

Question: Have you seen the LCD in action? 200cd is not bright but if it's got good contrast it'll prolly be fine.


Evan

evanh

I think you could reduce the clock rate down to close to 20 MHz and cut the blanking times to a minimum and still be in spec.

It says otherwise but you could also experiment with removing blanking altogether.


Evan

evanh

One word of warning. You have to be sure of everything you do. You should at least start with a working setup without a Prop. And get a decent scope in there so you can capture bunches of the signals to compare the Prop with.

This way you not only make sense of the datasheet but also have the confidence in doing the probing when you are trying to get the Prop to go.


Evan

evanh

Oh, holly Smile. It uses DE for all it's sync'ing. So, DE is basically a composite sync. And it doesn't use the H/V syncs at all.

With that in mind the minimums for DE will need to be observed.

But there is still no bottom limit the clock so there is a good chance you can get away with running at 20 MHz and have the vertical refresh below spec.


Evan

Sapieha

Sapieha said...
Hi grasshopper

Thanks for link.
It is fuly VGA compatible

So i translate this to "It will work". ill order up a few and make some boards. If it works out perhaps i can give away the remaining leftover prototypes.

Thanks so far but stay tuned, , ,Back to Top

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Nothing is impossible, there are only different degrees of difficulty.
For every stuipid question there is atleast one inteligent awnser
If you dont ask you wont know

Sapieha

grasshopper

Well back to the drawing board. It seems that all the above displays are obsolete. I Ask, there must be an IC that can drive all the displays that are using RGB in 8 to 16 bits?
I cant seem to find a solution, any one else trying to run a 5-7inch TFT and a propeller without having to purchase the small ones over at 4D

Timothy D. Swieter

Another thing to note here (and I am not trying to throw water on this idea) is the memory of the Propeller. The memory just isn't big enough for any decent color depth on larger size displays. Now, if you want to do monochrome or maybe four colors, then you might have enough memory for the larger screens. Of course this is all aside from the question of can the hardware drive it.

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Timothy D. Swieter, E.I.

www.brilldea.com·- Prop Blade, LED Painter, RGB LEDs, uOLED-IOC, eProto fo SunSPOT, BitScope
www.sxmicro.com - a blog·exploring the SX micro
www.tdswieter.com

grasshopper

Timothy D. Swieter said...
Another thing to note here (and I am not trying to throw water on this idea) is the memory of the Propeller. The memory just isn't big enough for any decent color depth on larger size displays. Now, if you want to do monochrome or maybe four colors, then you might have enough memory for the larger screens. Of course this is all aside from the question of can the hardware drive it.

Can you explain to me this notion of not enough memory? I am not sure why limits on memory would be a factor when I could hook up more to a pin on the propeller, right? Correct me if i am wrong but EEproms are cheap and well I seen people running a propeller using 2 gig memory drives. Would these devices be to slow?

Ale

grasshoper:

With 32 kbytes of memory, you can get 512x384 monochrome bit mapped with tiled color, as the example. For 640x240 monochrome, similar memory requirements. For 800x600... no dice, as 800x600 requires 60kbytes for the bitmap. Of course you can use only text mode (or mixed text and graphics) using less memory. Bigger resolutions not only need big bitmaps, but also big fonts (well, the parallax font is a savior here) and so on. I'm currently using a 640x480 panel as 320x240 (LCD), it is a dual scan so I have to produce both lines simultaneously... with one cog, it is very packed in timing, I should change to a 320x240 panel, but this setup... works!, and you know the rule, if it works, do not touch it, as I had enough trouble to get it working at all in the first place.
I was thinking in using a 800x600 panel as 400x300, but only when I understand how the pixel info is encoded (it has 2 8 bit ports, one for the upper part, one for the lower). It is sold for 15 euro at a discount shop here in Germany.

Edit: Link www.pollin.de/shop/produkt.php?ts=0&p=OTg4OTk4#MTI1OTc4OTk=

Question: The link points to a DSTN panel, it is possible that this panel only supports set or cleared pixels and thus shades of a color are only achieved with setting/clearing the corresponding pixel in a period of time (so the effective intensity is going to be the integral of the set time ?), and not with 6 or so bits to specify intensity ?... well I thought it worked differently....

Post Edited (Ale) : 9/16/2008 9:09:25 AM GMT

Timothy D. Swieter

What Ale said.

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Timothy D. Swieter, E.I.

www.brilldea.com·- Prop Blade, LED Painter, RGB LEDs, uOLED-IOC, eProto fo SunSPOT, BitScope
www.sxmicro.com - a blog·exploring the SX micro
www.tdswieter.com

Paul Baker

EEPROMs are not well suited for video buffering purposes, first they take a while to program which slows things down, also the I2C interface is quite slow itself, and the eeprom will be worn out relatively quickly by updating the contents so frequently. SRAM is the cheapest solution, but is not so easy to inteface with because it has so many pins. Typically some solution is done using helper chip(s) to drive those pins, like the Lattice CPLD used on the HYDRA Xtreme 512K SRAM card.

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

grasshopper

All right people thanks for the comments and teaching me more in the area of displays. I suppose ill have to wait for Prop II or get a different IC to power the video portion of my design.