STM32F207 direct drive of LCD

[oe2]

Posted on February 07, 2012 at 21:22

I'm up for a new project, to save money on the LCD we are looking in to use a realy sheep display without driver. The resolution is 480x286 so I guess to display a simple static GUI using the FSMC would not be a big problem. We plan to add external RAM to be used as video memory, and use DMA to lower the load on the CPU. However the pixel clock for the display must be around 9MHz. Have any one done someting simular using STM32F207?

#stm32f207-lcd-driect-drive

[emalund]

Posted on February 08, 2012 at 16:02

<i>sheep display</i> will it show the shephard too? :)

<i>However the pixel clock for the display must be around 9MHz. Have any one done someting simular using STM32F207?</i>

I do not know your sysclk speed, but something like sysclk/4 should be achievable with DMA. however, be aware that with a very heavy use of DMA there will only be few memory cycles left for the code

Erik

[Tesla DeLorean]

Posted on February 08, 2012 at 16:18

I think the word you're looking for is cheap. You mentioned a resolution, but not a physical size.

You should figure out what panel all the guys on eBay are using. They are clearly cheap, used in cell phones (ie high volume, low cost), and drivable with a simple DMA interface. You should look at how ST interfaces them, and what part they use, it's probably more expensive than you could find direct in China, so look for the equivalent displays.

The STM32 is not well suited to driving dumb panels, as it does not contain a LCD controller.

[oe2]

Posted on February 08, 2012 at 19:28

Sooory for the bad english... :)

However, I have found a Sharp 4.3inch display for 17USD, it need to be driven ''direct''. I have used STM32:s to my previus projects. I have tested to drive a 3.5inch display according to AN3241 to display ''static'' pictures. My concern is that the QVGA 3.5 inch display did only have a pixel clock at 3.6MHz (I used the same as in ST:s example) the new 4.3inch display have nearly 3times higher pixel clock. I'm planning to use a STM32F207 at 120Mhz bus speed. Do you have any suggestion for an other display with internal controller for less that 20USD??

[emalund]

Posted on February 08, 2012 at 20:20

Sooory for the bad english... :)

 

yours is MUCH better than many others, just could not help the smile and who does not need a smile now and then

Clive: The STM32 is not well suited to driving dumb panels, as it does not contain a LCD controller.

However, I have found a Sharp 4.3inch display for 17USD, it need to be driven ''direct''. I have used STM32:s to my previus projects.

There are ARM chips with a built-in LCD controller, you should be able to find one in the same price range as the STM32F2. I shall refrain from listing any at a ST website.

Erik

[oe2]

Posted on February 08, 2012 at 21:03

I know, problem is that I alredy have the stm32F207 and that the rest of the app is alredy written and ok... I planned to use an LCD with built in controller, but then I found the Sharp one...

[emalund]

Posted on February 08, 2012 at 21:24

I know, problem is that I alredy have the stm32F207

 

This, totally does not make sense.

If price is that important you must have a (somewhat) large production, and then ''having a chip already'' is irrelevant.  I have seen quite a few - very unpleasant - results from someone saving $10 in development cost and ending up with a huge cost from the result.

Erik

[Tesla DeLorean]

Posted on February 08, 2012 at 21:45

Sooory for the bad english... :)

 

However, I have found a Sharp 4.3inch display for 17USD, it need to be driven ''direct''. I have used STM32:s to my previus projects. I have tested to drive a 3.5inch display according to AN3241 to display ''static'' pictures. My concern is that the QVGA 3.5 inch display did only have a pixel clock at 3.6MHz (I used the same as in ST:s example) the new 4.3inch display have nearly 3times higher pixel clock. I'm planning to use a STM32F207 at 120Mhz bus speed. Do you have any suggestion for an other display with internal controller for less that 20USD??

 

Ok, so the physical size kills you for the price. As I mentioned, I don't think the STM32 is intrinsically very strong at LCD, it doesn't have an LCD controller, and it doesn't support SDRAM. There are clearly parts from NXP that would be a better choice.

People strapping these displays to STM32's are using SSD1963 controllers, which have memory on-board that can back the display directly. Could you add such a part, figure perhaps 7 USD, to the design?

Your direct drive display would take ~512KB of external memory on the STM32, figure 1MB if you need to switch images, half your bandwidth budget goes to reading the external memory, the other half to push at the display. Isn't the external bus on the STM32F2 60 MHz, which might support a 30 MHz display if it does nothing else.

[oe2]

Posted on February 09, 2012 at 14:34

What I mean with ''have alredy'' is that we alredy have done most of the development for the product on STM32. As I said erlier the plan was to use an display with internal controller...

[oe2]

Posted on February 09, 2012 at 14:49

The FSMC (Flexible Stiatic Memory Controller) in STM32 can drive NAND, NOR, SRAM and PSRAM. According to ST a static image in an external ram will result in a CPU load on approx 1%. (This is with a framerate of 40Hz and a 3.6Mhz pixel-clock on a QVGA)

http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/APPLICATION_NOTE/CD00278141.pdf

 page 11.

I cant seem to find where to by SSD1963 I have tried Digikey, Farnell/Newark, Mouser.

[emalund]

Posted on February 09, 2012 at 15:55

Changing horses in the middle of the stream

.... usually get you wet

I think you need to either bite the bullet and switch to another ARM or accept external display control

I do not think you will see a dramatic price difference between a 'dumb' display plus an external controller with associated components and a display with the same controller built in.

THUS, either switch to an ARM with a LCD controller or save a bunch of headaches and get the display and the controller as one package

Erik