RA8876 10.1 Inch Eastrising Display and Teensy 4.1 (SPI Issues)

[Paul96]

Hi Community,
this is my first post in this forum.

Setup:
I bought a 10.1 Inch Eastrising Display with the RA8876 chip quite some time ago and tested it on an ARDUINO Mega with the matching shield.
Everything was working properly.
I then wanted to change the MCU to a TEENSY 4.1 but I am now encountering (occasionally) problems with the display.

Issue:
After a couple of minutes after startup some of the characters on the display are suddenly rotated by 90 deg and some parts of the display start changing colors.
I have used the Oscilloscope on all SPI line (MISO, MOSI, SCLK, CS) and one thing I have noticed is that, whenever I connect the probe of the oscilloscope to the SCLK pin, the display gets corrupted the same way as described above.
Other than this issue, the signals itself look "sharp and in good shape"

Library:
RA8876_master
https://github.com/xlatb/ra8876

Wiring:
Pin 9 Reset
Pin 10 CS
Pin 11 MOSI
Pin 12 MISO
Pin 13 SCLK
3.3V to Backlight

Soldered directly to the pins with 10" long wires going directly to the Display pins (twisted and shielded)
Eastrising also recommended grounding the frame of the display and adding a capacitor on the Power Supply pins of the display (47uF). I did that

Code:
Demo Code from Library (ra8876-demo) with changed SPI pins


Question:
The display is the only SPI devices in my project. Do I need any termination/pullup resistors?
Has anyone else encounter this problem? What can I do to troubleshoot it further?
As mentioned above, connecting the probe of the oscilloscope to the SCLK pin causes the display to glitch in the same fashion.
I understand that the Oscilloscope has a certain resistance/capacitance -- maybe that's the issue even if the scope is not connected?

 

[thebigg]

Try reducing the SPI speed, perhaps the 10" long wires are too long.

 

[KurtE]

You also might try the library: https://github.com/wwatson4506/Ra8876LiteTeensy

 

[Paul96]

I tried reducing the Clock Frequency from 1MHz to now 300kHz.
I will do some testing and see if that worked.

I will try using the library in case the reduction in clock speed didnt work

 

[wwatson]

I tried reducing the Clock Frequency from 1MHz to now 300kHz.
I will do some testing and see if that worked.

I will try using the library in case the reduction in clock speed didnt work

Just a note, We found that reducing the interconnect wire length to 3" wires allowed 47Mhz SPI speed. The setting is found in RA8876_t3.h at about line 123.

// Default to a relatively slow speed for breadboard testing. 
//const ru32 SPIspeed = 47000000;
const ru32 SPIspeed = 3000000; --- default speed ---

Also I made sure to connect all of the ground connections on the display to the Teensy ground. Not sure if it is necessary. I can't remember now if others used just one ground wire...

 

[thebigg]

Also I made sure to connect all of the ground connections on the display to the Teensy ground. Not sure if it is necessary. I can't remember now if others used just one ground wire...

Yes. I needed to connect every GND pin on the 40 pin connector to Teensy GND to get reliable comms