I had EMI problems interfacing with my 4.0" ILI9488 v1.1 display over SPI. Having a long cable (about 30cm) display and touch works when powered using ST-Link V2, but when i powered it using a generic 24V PSU, the display and touch is not working all the time. Then I tried making the cables short to about 5cm, and added a low pass RC filter (letting 19MHz and below as my display SPI frequency is ~16MHz) the display now works flawlessly. But the touch is not working, there is an interrupt signal from the touch driver and data over SPI is being spit out but the frequencies I recorded are different. The correct frequency of 977KHz is there but there are smaller harmonic frequencies present on the SCK, MISO, and MOSI line.
Ps. I also added low pass RC filter of 1MHz cutoff frequency to the touch SPI MISO line but the lower harmonics are still present before and after I added the filter when I shortened the cables.
