51 MCU Tutorial Lecture 6_Serial Port Communication

STC51 microcontrollers usually have one serial port, and some have two serial ports. The serial port is generally used for downloading programs and serial communication. Serial communication is particularly suitable for controlling equipment, so industrial computers generally have serial ports.

The serial port pins of the 51 single-chip microcomputer are P3.0 and P3.1, which are RXD and TXD pins respectively. Serial port communication can be used for communication between single-chip microcomputers and other chips, communication between single-chip microcomputers, or communication between single-chip microcomputers and computers. Serial port communication is generally cross-connected. The standard serial port has 9 pins. In general, we only use RXD TXD GND. The remaining pins are communication control pins, which were used to control telephones in the past, but are basically not used now. Therefore, only RXD and TXD are retained on our 51 single-chip microcomputer.

The serial communication protocol is very simple. If the serial ports on the microcontroller are not enough, you can also use any two pins to simulate serial communication.

Generally, we use an 8-bit serial port protocol with a start bit. The baud rate is usually 9600, and there are also 1200, 2400, 4800, 115200, etc.

The program to open the serial port is as follows:
TMOD=0x20;
TH1=0xFD;
TL1=0xFD;
SCON=0X50;
TR1=1;
The program involves the configuration of 5 registers.
TMOD is the timer control register
TH1 and TL1 are the initial value registers of timer 1
SCON is the serial port control register
TR1 is bit 4 in the TCON register, because this register can be bit operated

The program for sending data through the serial port is as follows:
SBUF=55; // Send data 55
while(!TI);
TI=0;
The program involves two registers
SBUF is the serial port data register
TI is bit 1 in the SCON register, bit operation

The program for receiving data through the serial port is as follows:
if(RI)
{
recebuf=SBUF;
RI=0;
}
The program involves two registers.
SBUF is the serial port data register.
RI is bit 0 in the SCON register.

SBUF is both a transmit data register and a receive data register.

The above functional modules can be encapsulated into functions and called directly when used.