3 years, 10 months ago.

A ra8875 display module which also has the spi,but just all white on its screen

Hello David Smart,I mentioned your library one month ago and I am very interested in this kind of ra8875 based display,I have the same mbed board with you,LPC1768,and since I can't found your recommended screen module I bought a similar one,800 x 480,7.0'' TFT LCD, also drove by ra8875,and has a spi interface,and it also needs two 5 voltage power lines, I connected the circuit as your example pictures showed,and I tried every demo, but it only show a whole white screen,(If you only connected the power lines it wouldn't show anything,only when you have a program and the spi connection is right then the white appears ) I am a primary learner in this field,and I thought this for a long time and I still can't find a answer,I can be sure that all the connections is just right with your examples,what can be the probably reasons that this phenomenon occurred,and how could I solve them,I am quite confused?I will be very appreciate if you can answer my question,thanks! Charles /media/uploads/351056282/img_20170428_205725.jpg /media/uploads/351056282/img_20170428_205807.jpg

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2 Answers

3 years, 10 months ago.

You need a logic probe (cheap) or oscilloscope (getting cheaper) to find out if there is activity on the spi data pins. If there is no activity on the pins than its the code. Also look up on MBED examples of code that uses spi for your processor and compare your code against that. Just a guess, it looks like the display is not getting initialized properly.

Hey Darren thank you a lot for your attention,I will try this when I go to lab few days later.I think my mbed works just fine,but I can't make sure,I looked for some information that someone says the different frequency of SCK will also cause this problem,anyway thanks for your help

posted by Yu Charles 29 Apr 2017
3 years, 9 months ago.

hi Charles, I didn't spot this until just now. Have you solved your problem?

If not, what comes to mind is:

  • are you using the 5v version or the 3.3v version?
  • is your power supply clean? (do you have a scope in the lab to check it?)
  • you can change the frequency of the SPI interface, to slow it down, but the default is not fast.
  • You mention 2 supplies. You should only need 1 for the display. If you have the capacitive touch panel, I think you run a separate power for that, but let's leave that out of the picture until you have it working.
  • do you have the 4-wire SPI interface version, or the 3-wire? [The driver was written for and tested only with the 4-wire]
  • have you checked the jumper settings / solder blobs on the display module against the data sheet to make sure they are correct?

As Darren notes, if you have a way to scope it, then look at the signals and see if they are "clean" waves, transitioning for near zero to near 3.3v. Then you can double-check that the right signal is on the right pin on the display connector.

I hope one of these helps a bit.