Teensy 4.0 and ST7789V display

A bit of a long-shot, but has anyone had any success mating a PiMoroni ST7789V colour LCD with a Teensy 4.0?

I’m using the Adafruit_GFX / 7789 library, and a basic “hello world” demo sketch; the code works perfectly on a Uno, but when connected to the Teensy, although I can see the I/O lines waggling away, the display remains blank.

The device is marked “5V safe”, but I’m beginning to suspect it may be unhappy with the 3.3V logic levels of the Teensy 4 . . . but I can waggle the backlight on and off with a single I/O pin. Also, display is supposed to work with Raspberry Pi, which also has 3.3V logic.

The SPI speed remains the same as for the AVR (4MHz at the moment, but needs to go higher) - I think I need to have another session with the scope and compare the minimum timing requirements for chip-select and D/C, which are purely under software control.

It’s frustrating not being able to read back from the display, to at least try to verify register contents.

Turns out it is something of a Heisenbug - connecting 'scope leads cause it to work, so time to check the lead lengths.

Happily, not something buried deep in the SPI driver.

Edit: Simple fix - 100R series resistor on the SPI clock and data lines. Display is happy up to a nominal 80MHz clock rate