The st7735 is a display controller chip. There are a number of displays based on this controller chip on sale. Here I discuss the model I own. The st7735 is supposed by ucglib.
The ST7735 controller chip supports both parallel (8080-style) and serial (SPI) interfaces. When running in SPI mode, it uses SPI Mode 0, MSB-first. However, the board I own, and most I’ve seen online, are hard wires for SPI use. When using the SPI interface, it supports both 3 wire and 4 wire modes. The difference between 3 and 4 wire mode is whether the direction of the data is determined by a command or a pin. The display I own is wired for 4 wire serial mode.
For the board I own, as depicted above, the pinout is as follows. In the column “Board” is the marking on the board. In the column “Chip” is the name of the signal per datasheet. In the column “Signal” is the description of the channel.
|A0||WRX / D/CX||Direction:W/
|SCK||D/CX / SCL||SPI: SCK|
* The VDD voltage according to the datasheet is 2.6 to 3.3 Volt. However, the board appears to have a 3 pin component. It is likely to be a linear regulator. This would effect the acceptable voltage range. As a regulator regulated the voltage, the upper voltage might be higher, and as a regulator always has a dropout, the lowest voltage has to be increased by this dropout.