4" SPI TFT Display issues

[PaulF]

I have some 2.8" SPI touch screen displays with ILI9341 drivers which work perfectly using the brilliant Positron TFT Graphics library.
I also have some 4.0" SPI touch screen displays with ILI9486 drivers which I am having problems with.
They will not work if I select the drivers as ILI9486, however they do work if I select the driver as ILI9488? No real problem since they seem to work ok.
I also am having problems with the touch screen on these.
I have created a simple test program which indicates if the screen has been touched & to display the X & Y coordinates using "TftTouchGetCoordinates()".
It registers that the screen has been touched but the X & Y coordinates always return as 0.
The same program using the 2.8" display returns the correct coordinates.
I have tried 3 of the 4.0" screens with the same results.
I am new to using these screens so am sure I am missing something probably obvious, but I just can't see it at the moment.
Any pointers would be appreciated.

[trastikata]

Hi Paul,

take a look at the foot note here: https://picgraphic.com/TftLibrary2/ILI9488.html

Touch screen (1)
....
(1) Connect to different PIC MOSI pin.
The ILI9488 does not tri-state the MOSI line when CS is high, preventing other SPI devices that share the same MOSI line from operating correctly.

It means if the SPI line is shared between the ILI9488 and other devices, the 'other" devices might fail to read because ILI9488 does not release the MOSI line even if the CS pin is high.

Since the touch module uses only software SPI, you can connect the touch SPI MOSI pin to another PIC pin and set that in the library at initialization.


As for the correct driver IC - Chinese manufacturers mess these so often, label one thing, then it seems to be another.

[PaulF]

Thanks trastika, that makes sense.
It looks like I've been using an older version of the library which didn't have that footnote.
I thought it would be something simple that I'd missed.
You've saved me loads of head scratching.
Thanks again.