Thank you very much for your help. Here are the testing results:
Wiring
Serial output from "ST7789_readreg_diag.ino"
- select correct defines for your board wiring
- select correct interface type
- select appropriate report function
certain registers read first byte e.g. 0x00-0x0F, 0xDA-0xDC
other multi-argument registers read first byte as dummy
Bi-directional Read registers SDA (+ DC)
read reg(4): ID = 0x9104
controller
data sheet specific calls
controller reg(0x04) = 0x009104
controller reg(0x09) = 0x00610000
controller reg(0x0A) = 0x08
controller reg(0x0B) = 0x00
controller reg(0x0C) = 0x06
controller reg(0x0D) = 0x00
controller reg(0x0E) = 0x00
controller reg(0x0F) = 0xF0
controller reg(0xDA) = 0x00
controller reg(0xDB) = 0x91
controller reg(0xDC) = 0x04
Results of "GC9106_rotation.ino"
"GC9106_rotation.ino" seems to work perfectly.
Once again, thank you.