UART serial port

Embedded TFT LCD display module in the serial port, generally refers to UART port, UART, the full name of Universal Asynchronous Receiver/Transmitter.Serial port, that is, serial interface, corresponding to another interface called parallel port, parallel interface.Serial port is now the mainstream interface, a more representative to the number of Universal Serial Bus, Universal Serial Bus, that is, USB. Other serial interfaces commonly used in embedded LCD modules include I2C, SPI, rj-45, UART, USART, etc. 

The COM port

COM port is the asynchronous serial communication interface on the computer. The interface standard specification of COM port and bus standard specification are RS-232, sometimes called RS-232 port.

But now talk about UART port, COM port, RS232 interface, TTL interface between the relationship.

As we all know, UART interface and COM interface are physical interface, while TTL and RS232 are level standard (electrical signal).

The four pins of UART correspond to TTL level, with low level 0(0V) and high level 1 (3.3v or above).

Uart serial port features

The serial port controller is a single chip microcontroller that writes a serial port communication program. In most cases, the uart controller is all done together with the CPU in the embedded system.

Pin introduction (COM port is more pin, but these are also commonly used) :

VCC: power supply pin, generally 3.3v,

GND: ground pin,

RX: receive data pin

TX: send data pin

Characteristics of the COM

Com ports usually have 9 pins, but they also have 25 pins.Usually used to connect the mouse and communication equipment

Current mainstream motherboard takes a serial port commonly, do not take even, can be replaced by USB slowly.

COM port pin introduction

9 pin drawing of serial port

Pin function of 9-pin serial port:

Stitching function

1 carrier detection (CD)

2 receiving data (RXD)

3 sending data (TXD)

4 data terminal ready (DTR)

5 signal ground wire (SG)

6 data ready (DSR)

7 request sending (RTS)

8 clear send (CTS)

9 ringing indication (RI)

25-pin interface definition:

The Pin 1 Protective Ground

Pin 2 Transmit Data

Pin 3 Received Data

Pin 4 Request To Send

Pin 5 Clear To Send

Pin 6 Data Set Ready

The Pin 7 Signal Ground

Pin 8 Received Line Signal Detector

(the Data Carrier Detect)

Pin 20 Data Terminal Ready

The Pin and Ring Indicator

TFT LCD Display Module serial port usage:

We often use UART port for debugging, but the UART data to be passed on to the computer analysis to match the computer interface, usually we use computer and USB interface has the COM port (in the end is a virtual COM port on the computer), but if you want to connect the two interface will need to convert the hardware interface and virtual interface level conversion.

If the computer COM port is connected, a small conversion board is needed, which realizes the TTL level and RS232 level interconversion.                 

If you want to connect the USB interface, also need a small conversion board, it implements the TTL level and USB level conversion, this is a relatively common interface conversion.


The circuit diagram and connection are shown below, usually with a dedicated conversion chip.



1. Serial port and COM port refer to the physical interface form (hardware).TTL, rs-232, and rs-485 refer to the level standard (electrical signal). 

2. Generally, GND, RX and TX are connected to the device.Do not connect Vcc or +3.3v power cord to avoid power supply conflict with the target device. 

3. PL2303 and CP2102 chips are USB to TTL serial port chips, using USB to expand the serial port (TTL level)

4. MAX232 chip is a special bidirectional conversion chip between TTL level and RS232 level, which can be used to convert TTL to rs-232 or rs-232 to TTL. 

5. TTL standard is 0 for low level and 1 for high level (+5V level).Rs-232 standard is positive level is 0, negative level is 1 (15V level). 

6. Rs-485 is similar to rs-232, but adopts negative logic of differential signal. 

The Relationships Between The Various Interfaces In The LCD Display Module