There are several ways of connecting MCU (Microcontroller Unit) or MPU (Microprocesser Unit) or CPU (Central Processing Unit) with LCD, SPI interface is one of them.

Fig. 1 Connection Between MCU to LCD

Basic knowledge introduction (1):LCD Driving Waveform

LCD can’t be driven with DC (Direct Current), it has to be driven with AC (Alternative Current) and the overall current has to be ZERO. Otherwise, the Liquid Crystal Material will be damaged sooner or later.

Fig. 2 LCD Driving Waveform

Basic knowledge introduction (2):LCD Controller vs Driver

There are two types of Driver IC’s, Common Drivers and Segment Drivers. Common Drivers output signals to create the rows or numbers of lines. The Segment Drivers output the necessary signals to create the characters or columns.

The Controller IC receives data written in ASCII or JIS code from the MPU and stores this data in RAM. This data is then converted into serial character patterns and transferred to the LCD driver IC.

Drive/Controller IC is probably the most commonly found in a graphics module. This IC receives data from the MPU and stores it in RAM. Also, it accepts commands directly from the MPU for both the common and segment drivers.

SPI Interface

SPI (Serial Peripheral Interface Bus) includes the following 4 wires:

SCLK: serial clock (output from master);

MOSI： master output, slave input (output from master);

MISO： master input, slave output (output from slave);

SS: slave select

Used in Mono digit, character, graphic LCD, small TFT, some CTP

Fig. 3 4 Wire SPI Interface

Fig. 4 4 Wire SPI Interface

For SPI related products, you can also find it here.

TFT color display

TFT module-with PCB board

Graphic LCD module

segment LCD display

OLED module