Using TFT LCD?

[lpcware]

Content originally posted in LPCWare by james on Sun Apr 29 22:29:04 MST 2012
Hi,

I am trying to create a graphical user interface using a 24bit 4.3inch TFT LCD touchscreen, but I am not sure of a good way to do this.

Basically, I need to supply a pixel clock of at least 5mhz, and change 24bits of GPIO under 83ns.

Using timer interrupts would load up the processor so much that I do not think it will be able to process other functions. What would be a good or rather correct way to do this?

edited:

Just for more information, the TFT LCD is http://www.startek-lcd.com/te_product_g/2012-03-02/1834.chtml .

Can this be driven by a 1768 running at 100mhz directly (no graphic chip) and yet support other functions such as uIP and rs485 communication?

[lpcware]

Content originally posted in LPCWare by frame on Fri May 04 04:14:07 MST 2012
Could your wiring be inapproriate, i.e. too long ?
(Didn't see your video, my cpy block youtube access ...)
An 5MHz square wave signal has harmonics well into the UHF range.

I would try to match the wave impedance of the wiring and the LCD panel input as good as possible. Otherwise you might get reflections that could produce such a shakey appeareance

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Quote: james
Finally got my LCD to sync but at a much lower rate than the lcd datasheet said.
1mhz pixel clk instead of recommended minimum of 5mhz

The screen is very "shakey", here a clip at:
http://www.youtube.com/watch?v=aUSD0ZJDx44

Could someone with experience in using LCD give some advise for improving the display?

Is this cause by a Vsync problem or something else?

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[lpcware]

Content originally posted in LPCWare by daan-ter-horst on Fri May 04 03:25:29 MST 2012

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Quote: js-nxp
This is what I get with a 7" display with a LPCXpresso in 16 bit mode at 48MHz
https://vimeo.com/34993666

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where did you buy this display??

[lpcware]

Content originally posted in LPCWare by james on Fri May 04 02:02:30 MST 2012
Finally got my LCD to sync but at a much lower rate than the lcd datasheet said.
1mhz pixel clk instead of recommended minimum of 5mhz

The screen is very "shakey", here a clip at:
http://www.youtube.com/watch?v=aUSD0ZJDx44

Could someone with experience in using LCD give some advise for improving the display?

Is this cause by a Vsync problem or something else?

[lpcware]

Content originally posted in LPCWare by james on Thu May 03 07:22:21 MST 2012
Okay finally got my LCD to show "something" using pwm to trigger a 5mhz pixel clk but i  am having sync problems.

Is there anyway i can count the number of pulse from the pwm? I can't use timers as the mcu would be serving the interrupts all the time that it can barely do anything else.

I need to control the Hsync and Vsync clock pulse signals in respect to certain number of pixel clk, what would be a good or correct way to do this?

[lpcware]

Content originally posted in LPCWare by js-nxp on Tue May 01 20:30:40 MST 2012

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Quote:
may I know which pin/function you are using to drive the pixel clock?

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I'm not driving the pixel clock, the driver chip (SSD1963 for the 7" display, can't remeber the chip for the 3.5" :p ) does all that.

I'm using 12 bits from GPIO2 and 4 bits from GPIO1 rotating and oring them for the 16 bits data, a bit messy but it works.

The 8 bit version just 8 bits from GPIO2.

[lpcware]

Content originally posted in LPCWare by james on Tue May 01 19:08:01 MST 2012

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Quote: js-nxp
This is what I get with a 7" display with a LPCXpresso in 16 bit mode at 48MHz
https://vimeo.com/34993666

It would be faster if I could manage to get 16 consecutive bits with the chip :mad:

A bit better with a 3.5" display
https://vimeo.com/34178528

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Great video, may I know which pin/function you are using to drive the pixel clock?

[lpcware]

Content originally posted in LPCWare by james on Tue May 01 18:43:11 MST 2012
Thanks guy for replying,

I have checked with the supplier and he sent me the datasheet for OTA5180A.

Oh wow! I seriously did not think of so many factors to consider for designing a 480x272x3 TFT LCD interface, I can't really find any good sources that explains how to use/program/interface a TFT LCD, due to its common use in consumer electronics search returns in google always ends up with advise for the general consumers....

Could someone post some sources of design guide for interfacing/using a TFT LCD with a MCU with or without external driver chip?

Thanks aplenty! :)

[lpcware]

Content originally posted in LPCWare by js-nxp on Tue May 01 14:41:26 MST 2012
This is what I get with a 7" display with a LPCXpresso in 16 bit mode at 48MHz
https://vimeo.com/34993666

It would be faster if I could manage to get 16 consecutive bits with the chip :mad:

A bit better with a 3.5" display
https://vimeo.com/34178528

[lpcware]

Content originally posted in LPCWare by frame on Tue May 01 03:23:21 MST 2012
For a LCD board with driver chip, you would need a hardware memory interface to drive it directly with memory accesses.

Otherwise, you would just need patience. I have a sample driver project for the EA QVGA display, driven by GPIO in 8 Bit mode. The fastest implementation is on a STM32F4 with 168MHz, which still needs about 2 seconds to fill the screen. I consider this sufficient for text and a few graphics elements, but not GUIs.

[lpcware]

Content originally posted in LPCWare by js-nxp on Mon Apr 30 23:57:08 MST 2012
The sales pitch mentions Drive:OTM5180A so it MAY have a driver chip, however I can't find any data sheet for that chip, maybe it is compatible with other chips.

The OTM3225A is used in some TFT LCD it seems.

[lpcware]

Content originally posted in LPCWare by rocketdawg on Mon Apr 30 13:20:47 MST 2012
it is not the speed, but the frame buffer.
480 x 272 x 3 (RGB) is a big number of bytes.  You need external RAM.