How to organize serial communication SerialPort in. NET 2.0

. NET 2.0 Serial Communication Class SerialPort usage sorting

1. Introduction

With the popularity of USB, serial communication has been applied to many aspects of daily life. USB is a high-speed serial communication protocol, and the USB interface is very complicated, it is usually used in places where a large amount of data needs to be transmitted.
Such as USB flash drives, cameras, and printers. In addition to USB, the more luxurious serial port, in industrial control and embedded industry, a large number of use is another ancient serial port protocol, RS-232 serial port. RS-
232 is a very simple low-speed serial communication interface that can receive and send data at the same time.

2 .. NET 2.0 support for serial ports

. NET 2.0 provides support for the serial communication function. You can find related classes under the namespace system. Io. ports. The most important of these classes is the SerialPort class.

By creating a new SerialPort object, we can control the whole process of serial communication in the. NET program.

3. Use SerialPort to set serial port Properties

For serial communication, you need to set some relevant parameters. You can set the SerialPort class attributes. Serial Port attributes mainly include

. Portname serial port name, COM1, com2, etc.
. Baudrate baud rate, that is, the speed of serial communication. The baud rate of both parties for serial communication must be the same. If you use a PC to connect to other non-PC systems, generally, the baud rate is determined by the non-PC system.
. Parity parity. You can select values in the enumerated parity.
. Databits data bit
. Stopbits stop bit. You can select the value in the enumerated stopbits.
. Handshake handshake mode, that is, data stream control mode, you can select the value in the enumeration handshake

4. Enable and disable the serial port

After creating a SerialPort object and setting the serial port properties, you can open the serial port through the open () method. After data is read/written, you can close the serial port by using the close () method.

Based on experience, for some systems, after enabling the serial port, you also need to set rtsenable to true to read and write data. Otherwise, data cannot be read and written normally.

5. Read/write row data

When both parties communicate, they generally need to define the communication protocol, even though the simplest program that sends text chat through the serial port.

Generally, when one party presses the carriage return, it sends the text of the data together with the line break to the other party. In this communication case, the Protocol Delimiter is defined by a line break, and each token data is separated by line breaks, so that it is easy to identify the information sent by the dual-sending communication.

In the preceding example, you can use writeline () to send data and Readline () to read data. After writeline sends the data, it will also send the line break as the data
To the other party. When Readline () is used to read data, a linefeed is returned, indicating a row of information. You can use the SerialPort
Newline. In general, Windows uses crln as a line break, while in Linux, linefeed is represented by only one ln.

The Readline () method is blocked until a line break is returned. If the line break is not encountered during data reading,
Timeoutexception. By default, readtimeout is infinitetimeout. In this way, Readline is always in the blocking status,
Until a new row of data arrives.

The writeline () method is also blocked. If the other party cannot receive data in time, it will cause a timeoutexception exception.

Since the Readline () and writeline () methods are both blocking, when the program uses SerialPort for serial communication, read/write operations should generally be handled by other threads, avoid program non-response due to blocking.

6. Read/write bytes or character data

For bytes or character data, the read () method is used to read data. This method requires a byte or character array as a parameter to save the read data, returns the number of bytes or characters actually read. Use the write () method to write data. This method can send byte arrays, character data, or strings to the other party.

If both parties need to build a serial communication program to exchange data bit byte stream data, the two parties should define the data segment format. Generally, the data sequence is defined by the sequence header and the sequence end.

Sending data is relatively simple. You only need to send the constructed data using the write () method.

Receiving data is complicated, and communication is in the form of byte streams. Calling the read () method once does not ensure that the data read is complete. Therefore, you need to integrate the data read each time in
To analyze the integrated data. According to the defined bytes format, the bytes information is extracted from the byte stream through the Expires header and the suffix, so that meaningful information can be obtained.

In addition to using the read () method to read data, you can also use the readexisting () method to read data. This method reads the data that can be read and returns the data in the form of a string.

7. Event

SerialPort provides datareceived events. This event is triggered when data enters. The trigger of this event is determined by the operating system. When data arrives, this event is triggered in the auxiliary thread. The priority of the auxiliary thread is relatively low. Therefore, this event cannot be triggered when data in each byte arrives.

When using this event to receive data, it is best to define the communication protocol format and add the Expires header and expires tail. When receiving data in a datareceived event, the data is cached in an array or a string. When the received complete data contains the Expires header and the end of the expires, it is processed. In addition, to effectively receive data, you can add system after each data read. threading. thread. sleep method.

8. Others
Use a jumper to connect the 2nd and 3 pins of the serial port to Realize Serial Communication on the local computer. Therefore, the program can be detected through the 2nd and 3 pins of the serial port.

 

. Bytestoread this attribute returns the number of bytes that can be read.

Method Name	Description
Close	Close the port connection, set the isopen attribute to false, and release the internal Stream object.
Open	Open a new serial port connection
Read	Number of bytes read from the SerialPort input buffer
Readbyte	Synchronously reads one byte from the SerialPort input buffer
Readchar	Synchronously read one character from the SerialPort input buffer
Readline	Reads the newline value from the input buffer.
Readto	Reads the string of the specified value in the input buffer all the time.
Write	Overloaded. Write Data to the output buffer of the serial port
Writeline	Writes the specified string and newline value to the output buffer.

Discardinbuffer Discardoutbuffer

Clear Received Buffer data Clear output buffer to data

Attribute description

Name	Description
Basestream	Obtain the basic Stream Object of the SerialPort object
Baudrate	Get or set the serial baud rate
Breakstate	Obtains or sets the interrupt signal status.
Bytestoread	Obtain the number of bytes of data in the receiving buffer.
Bytestowrite	Obtains the number of bytes of data in the sending buffer.
Cdholding	Obtains the status of the Carrier Detection Line on the port.
Ctsholding	Obtain the status of the "sendable" Row
Databits	Obtains or sets the length of standard data bits for each byte.
Discardnull	Gets or sets a value that indicates whether null bytes are ignored during transmission between the port and the receiving buffer.
Dsrholding	Obtain the status of the data set-up (DSR) Signal
Dtrenable	Gets or sets a value that enables DTR signals during serial communication.
Encoding	Obtains or sets the byte encoding for text conversion before and after transmission.
Handshake	Obtains or sets the handshake protocol for serial port data transmission.
Isopen	Gets a value indicating whether the SerialPort object is enabled or disabled.
Newline	Gets or sets the value used to explain the end of the call of the Readline () and writeline () methods.
Parity	Obtain or set the Parity Check protocol

Parityreplace	Gets or sets a byte that replaces the invalid byte in the data stream in case of a parity error.
Portname	Obtains or sets communication ports, including but not limited to all available COM ports.
Readbuffersize	Gets or sets the size of the SerialPort input buffer.
Readtimeout	Gets or sets the number of milliseconds before the read operation has timed out before it has been completed.
Receivedbytesthreshold	Obtains or sets the number of bytes in the input buffer before the datareceived event occurs.
Rtsenable	Gets or sets a value indicating whether to enable the request sending (RTS) signal in serial communication.
Stopbits	Obtains or sets the standard stop bits for each byte.
Writebuffersize	Obtains or sets the size of the serial port output buffer.
Writetimeout	Gets or sets the number of milliseconds before the time-out occurs when the write operation is not completed.