I was feeling elated by my success with the FYSETC mini 12864 panel and I tried my old “REPRAP Discount Graphics” panel. I thought “surely this should work as well it’s the same SPI graphics LCD after all”.
We you guessed it – work it did not. I tried software SPI, hardware SPI, nothing. Looks like I had to read the manual. Shame!!!
Here is what I found. The old “discount graphics lcd” is not quite the same chip. It uses ST7920 controller, which is a supreme oddball. It uses some very strange scheme and transfers data 4 bits at a time.
Then I remembered I had added support for hardware SPI for that chip since PrntrBoard V1. Why was it not working?
Well, it was because for some strange reason the data pins on the panel are not connected to the SPI interface on the EXP2 connector, so the u8g library has to use software SPI emulation and I didn’t add support for that.
So fixed that, now I have both hardware support and software emulation for the st7920 driver and here it is working:
Next I’m waiting on some 2004 LCD screens to arrive. These should be easier, since there is no hardware protocol involved.