Regarding Serial Port Screen

Serial port screen is one kind of display solutions consisting of a microcontroller or PLC with a controller. The communication part of the display solutions includes serial communication protocol, UART serial port or SPI serial port, etc.

The serial screen can receive instructions sent by the user's microcontroller serial port and complete all setting for UI/drawing on the display screen. The serial screen includes hardware and software sections, The hardware part includes lcd screen, touch panel, controller, FLASH storage, RS232 or 485 serial port chip, audio and video decoding chip, SD card slot, etc. Some models include WIFI, 4G, bluetooth, voice/face/fingerprint recognition etc, among these components, the controller play the highest role in performance for the display screen. The operating software is generally divided into two parts, namely "system software running on the serial screen hardware" and "screen configuration software running on PC Windows operating system". Customer need firstly use the screen configuration software of serial port screen to create a "project file", and then download the prepared "project file" to the controller of serial port screen through serial port on PC and the screen, SD card, U disk, etc. And run in screen's Flash.

Serial port screen is unlike parallel port screen, it has some different function, firstly the baud rate achieve 115200 bps. Secondly it could use USB2.0 port to burn UI on the Flash, very convenient for customer to update project. Thirdly, customer could set the program based on computer, very easy to design UI graphic. Fourthly, serial port screen support about 70 serial port commands, such as displaying images, progress bar, touch bar control, button control, text display, virtual touch, drawing graphics etc.

The reason why serial port screen is convenient for customer's second development is that serial port screen could receives the instructions sent by the serial port of customer's computer, and could completes all operations of drawing on the display. At the same time, the user's touch operation on the display is sent to customer through the serial port.

The serial port include I2C, SPI and UART, each interface has the features as below.

I2C (Inter IC bus) interface is often used to transmit data between two ICs, and the amount of transmitted data is small (such as EEPROM, capacitive screen applications, etc.). The advantages is simple, few communication pinout, only needs two wires: SDA (serial data line) and SCL (serial clock line), to transfer information between devices. The disadvantages is slow transmission speed, half-duplex. It transmit data between two wires through complex logical relationship, even in HS (high speed mode) only 3.4Mbps, that is 3.4M/8 = 435KB/s.

SPI (Serial Peripheral Interface, Serial Peripheral Interface) is a full-duplex synchronous serial bus developed by Motorola, which is widely used with slow peripheral devices such as EEPROM, ADC, FRAM and display drivers communication. The advantage is full-duplex, the transmission speed is much higher than IIC, the highest can reach 50Mbps, converted into bytes is 50Mb/8=6.25MB/s. The disadvantage is, compared with the high-resolution display screen, requirement on transmission speed cannot be met. For example, for a 320*480 TFT display screen, a complete picture needs to transmit at least 320*480*16=2,457,600bps. If 24 frames of pictures are to be transmitted per second, it needs 58,982,400bps, which is far beyond the maximum transmission of the SPI interface speed (the maximum speed of SPI interface of ILI9488 is only 20MHZ). So SPI interface is more commonly used for low-resolution displays, such as 240x320 or smaller.

UART interface is Universal Asynchronous Receive Transmitter, which is a serial communication of two-wire protocol. The data cable signal wires are labeled Rx and TX. This protocol is used to send and receive data and clock pulses byte by byte. It is a full-duplex protocol, means that data is sent and received at different rates simultaneously. Different devices communicate with the microcontroller through this protocol. The advantages is long transmission distance, RS232 can reach 15 meters, RS485 can reach 3000 meters. The disadvantages is low transmission rate, RS485 has a maximum of 10Mbps, while RS232 or TTL has a maximum of 1.43Mbps. Generally speaking, UART refers to a communication protocol, which has various level standards: TTL, RS232, RS485, RS422 serial signal.

a. TTL: low level 0 (0V), high level 1 (3.3V or above)

b. RS232: low level 0(+3~+15V), high level 1(-3V~-15V)

c. RS485/RS422: low level 0(-2~-6V), high level 1(+2V~+6V)

Serial port screen is mainly for small microcontroller solutions with limited resources or performance, such as 8051, AVR, PIC, MSP430, Z80, ARM and other low-cost solutions. Also it's suitable for Arduino open source hardware platforms, ESP32 and other objects Network development hardware platform. The application could be smart home appliances, coffee machine, pos device and communication device etc.