HX8357 TFT Display Goes white screen when serial port opened Solved

I have a 3.5" Adafruit TFT display and an STMPE610 Board connected to an Arduino Mega2560. Wired up a breadboard to use the SPI interfaces and eventually got the test display to work as well as the touch screen. However, they only work without a serial connection to the Mega. I used the small test program graphicstest from the tutorial with a small bit of code to read the touch screen and that runs, again only with the mega disconnected from the computers usb port. If the TFT is displaying properly and I plug in the usb port the display goes white screen, although I still get touch output.

I have no clue as to what the issue is here and don’t see anything similar in the forum so decided to post this. Code attached.

I now do have a clue from some discussions regarding MISO on some TFT’s not supporting tri-state so I switched the STMPE610 to I2C I/F and now everything works as it should with the usb port in use. Can’t find any docs that indicate that the 3.5" TFT display has that problem but something was definitely amiss.

TFTtestv1.ino (12.9 KB)