3-Wire SPI Explained
Intro I'm working on a new PCB project with a SSD1306 128x64 OLED display and was curious to try using 3-wire SPI mode. It's not a new subject for me, but I wanted to try using it to gain speed rather than have it slow things down (e.g. bit banging the protocol). Some background information is required before I share the project details. Small Displays Small displays like the SSD1306 and color LCDs like the ST7789 from Sitronix support updating their internal display RAM over a serial (SPI) connection. The display controllers understand "commands" and pixel data. The commands serve to configure the controller and move the write pointer (where the pixel data gets written). In order to know if incoming serial data should be interpreted as commands or pixels, the controllers have a D/C (data/command) signal. This can either be a separate signal wire or encoded into the data stream. When it's a separate signal, this is referred to as "4-wire SPI". The 4 wire