Can the STM32F769 drive/control a ''dumb'' TFT LCD?

[Shayan D]

Posted on March 28, 2018 at 19:01

I'm trying to interface an STM32F769 with a 4.3' 480 x 272 TFT LCD via a parallel 16 bit RGB interface. Some of these TFTs have built in controllers/drivers, like an OTA5180A, HX8227, or a SSD1289, while other 'dumb' TFTs have no built in controller/driver. I'm trying to figure out if I can use a display without any built in controller/driver. I've read the AN4861 app note, but I'm still a bit confused... I think I may be getting driver and controller mixed up. The LTDC peripheral is just a controller, and a TFT with a built in driver is still necessary?

Will the built in LTDC peripheral of the STM32F769 be enough to interface with a TFT LCD that has no built in driver/controller? 

Thanks for your help.

#rgb #tft-lcd #stm32f769

[waclawek.jan]

Posted on March 29, 2018 at 10:35

The '769 is intended to be connected to LCD through a MIPI/DSI interface. For 'normal' (parallel RGB) interfaced LCD, use a '767.

The LCD pins may all be there on a larger '769 package (it's upon you to check), but why would you pay the extra for the MIPI module which you won't use?

JW.

[Shayan D]

Posted on March 29, 2018 at 17:42

That's a good point. I mention the 769 since there's an evaluation board available for it, but we will probably use the 767 once we make our own board. 

[markus239955_stm1_stmicro_com]

Posted on March 29, 2018 at 14:42

> I think I may be getting driver and controller mixed up.

Driving a TFT consists on 3 stages:

- analog drivers

- digital drivers

- framebuffer storage

The analog drivers address all pixels on an TFT to convert the digital pixel data to analog voltage levels. There are the line and row drivers and also the voltage generator of the different analog TFT supply voltages.

The digital drivers control the timing of data packages send to the analog drivers to generate a image on the TFT.

The framebuffer storage contains the pixel data and is read by the digital drivers.

The STM32 with LTDC fulfills the functionality of the framebuffer storage and digital drivers. A dumb TFT with only analog drivers (mostly on glass chips on the TFT integrated by the manufacturer) are a good match. Large TFTs (>4') often need additional driving voltages created by external components, because the onboard analog drivers do not generate them.

Some TFT controller ICs like the ones mentioned above fulfill all 3 stages to drive a TFT, so the host CPU only needs to fill the external framebuffer with new pixel data. The TFT controller offers a data interface to the CPU instead of a timing constrained direct driven TFT interface.

On the STM32F429i-disc1 is a hybrid solution, the ili9341 where you can configure over SPI if the ili9341 fulfills all 3 stages or if the LTDC fulfills the digital stages and the ili9341 drives the analog stage.

It is up to you to select the best hardware for your needs, its always price vs performance.

[Shayan D]

Posted on March 30, 2018 at 02:24

Thanks!

horbach.markus wrote:

The STM32 with LTDC fulfills the functionality of the framebuffer storage and digital drivers. A dumb TFT with only analog drivers (mostly on glass chips on the TFT integrated by the manufacturer) are a good match.

If possible, could you give me an example of one of these TFT displays (any size) with only analog drivers built in? Or could you give me the name of a common analog only driver IC? I just want to check the block diagram of one these drivers for reference.

[markus239955_stm1_stmicro_com]

Posted on March 30, 2018 at 08:10

Have a look here:

http://www.newhavendisplay.com/tfts-c-1.html

 

I used a innolux at070tn with 24bit parallel interface for a project with an STM32f429.

[AVI-crak]

Posted on March 29, 2018 at 19:39

STM32F769 can not.

The stupid TFT LCD panel has an incredibly low price tag, as well as very simple operation. Glass 7 inches TFT panels (not the whole package !!!) has a cost less than two dollars, the collected package has a price less than three dollars. Such a low price is achieved by the incredible stupidity of the panel.

There is no power regulator - an external voltage driver is required, for example

https://community.st.com/external-link.jspa?url=http%3A%2F%2Fgolf2109.blogspot.ru%2F2018%2F02%2Fboost-regulator.html

.

There is no DAC - external shaping of RGB analog signal is required.

There is no correction of color space distortions - this you need to take care of yourself.

By the same, all the stupid TFT LCD panels are divided into two distinct groups: progressive scanning, interlaced scanning.

Without a big headache, you can use stupid TFT LCD panels with progressive scanning. They have a multiple resolution! television standard.

Otherwise, you will have to use an ancient controller like TW8806 - he knows how to break the flow into parts.

Additionally, the external RGB signal driver changes the polarity of each full frame. This can be done on one transistor, but it's better when the controller can do it.

Thus - wild savings on a stupid TFT LCD panel can affect the size and initial cost of development. And also with the huge difficulty of buying a large batch of glass.

You can experiment with faulty home appliances - where there's a 7-inch panel. This portable DVD players, 2 DIN radio tape recorders, portable TVs and so on. Experiment with the purpose of learning more about this interface.