This example illustrates how to communicate with a serial port instrument by writing and reading text data. The instrument is a Tektronix TDS 210 two-channel oscilloscope connected to the COM1 port. Therefore, many of the following commands are specific to this instrument. S = serialport, without arguments, connects to the serial port using the property settings of your last cleared serialport object instance. The retained properties are Port, BaudRate, ByteOrder, FlowControl, StopBits, DataBits, Parity, Timeout, and Terminator.

Controlling Access to the MATLAB Command Line

You control access to the MATLAB command line by specifying whether a read or write operation is synchronous or asynchronous.

A synchronous operation blocks access to the command line until the read or write function completes execution. An asynchronous operation does not block access to the command line, and you can issue additional commands while the read or write function executes in the background.

The terms synchronous and asynchronous are often used to describe how the serial port operates at the hardware level. The RS-232 standard supports an asynchronous communication protocol. Using this protocol, each device uses its own internal clock. The data transmission is synchronized using the start bit of the bytes, while one or more stop bits indicate the end of the byte. For more information on start bits and stop bits, see Serial Data Format. The RS-232 standard also supports a synchronous mode where all transmitted bits are synchronized to a common clock signal.

At the hardware level, most serial ports operate asynchronously. However, using the default behavior for many of the read and write functions, you can mimic the operation of a synchronous serial port.

Note

When used in this guide, the terms synchronous and asynchronous refer to whether read or write operations block access to the MATLAB command-line. In other words, these terms describe how the software behaves, and not how the hardware behaves.

The two main advantages of writing or reading data asynchronously are:

• You can issue another command while the write or read function is executing.

• You can use all supported callback properties (see Events and Callbacks).

For example, because serial ports have separate read and write pins, you can simultaneously read and write data. This is illustrated in the following diagram.

Serial port name, specified as a character vector or string. The seriallist function provides a list of available serial ports. You must specify the port to create a serial port object.

The port name depends on the platform that the serial port is on. This list is an example of serial constructors on different platforms:

Example: s = serial('COM1')

Data Types: charstring

Name-Value Pair Arguments

Specify optional comma-separated pairs of Name,Value arguments. Name is the argument name and Value is the corresponding value. Name must appear inside quotes. You can specify several name and value pair arguments in any order as Name1,Value1,.,NameN,ValueN.

For a list of serial port object properties that you can use with serial, refer to Property Reference.

Note

Port must be the first argument used to create the serial object. You can then follow port with any number of supported name-value pairs.

Rate at which bits are transmitted, specified as the comma-separated pair consisting of 'BaudRate' and a double. You configure baud rate as bits per second. The transferred bits include the start bit, the data bits, the parity bit (if used), and the stop bits. However, only the data bits are stored.

The baud rate is the rate at which information is transferred in a communication channel. In the serial port context, 9600 baud means that the serial port is capable of transferring a maximum of 9600 bits per second. If the information unit is one baud (one bit), the bit rate and the baud rate are identical. If one baud is given as 10 bits, (for example, eight data bits plus two framing bits), the bit rate is still 9600 but the baud rate is 9600/10, or 960. You always configure BaudRate as bits per second.

Note

Both the computer and the peripheral device must be configured to the same baud rate before you can successfully read or write data.

Standard baud rates include 110, 300, 600, 1200, 2400, 4800, 9600, 14400, 19200, 38400, 57600, 115200, 128000, and 256000 bits per second.

You can also set the BaudRate property after creating the serial object using this syntax:

Example: s = serial('COM1','BaudRate',4800);

Data Types: double

Byte order of the device, specified as the comma-separated pair consisting of 'ByteOrder' and littleEndian or bigEndian. If ByteOrder is littleEndian, the device stores the first byte in the first memory address. If ByteOrder is bigEndian, the device stores the last byte in the first memory address.

For example, suppose the hexadecimal value 4F52 is to be stored in device memory. Because this value consists of two bytes, 4F and 52, two memory locations are used. Using big-endian format, 4F is stored first in the lower storage address. Using little-endian format, 52 is stored first in the lower storage address.

The byte order of littleEndian is the default and is used in read and write operations if you do not specify the property. You need to specify the property only to change the byte order to bigEndian.

You can also set the ByteOrder property after creating the serial object using this syntax:

Note

Configure ByteOrder to the appropriate value for your device before performing a read or write operation. Refer to your device documentation for information about the order in which it stores bytes.

Example: s = serial('COM1','ByteOrder','bigEndian');

Data Types: charstring

Number of data bits to transmit, specified as the comma-separated pair consisting of 'DataBits' and 5, 6, 7, or 8, which is the default. Data is transmitted as a series of five, six, seven, or eight bits with the least significant bit sent first. At least seven data bits are required to transmit ASCII characters. Eight bits are required to transmit binary data. Five-bit and six-bit data formats are used for specialized communications equipment.

Note

Both the computer and the peripheral device must be configured to transmit the same number of data bits. Apple mac address book download.

In addition to the data bits, the serial data format consists of a start bit, one or two stop bits, and possibly a parity bit. You specify the number of stop bits with the StopBits property, and the type of parity checking with the Parity property.

You can also set the DataBits property after creating the serial object using this syntax:

Example: s = serial('COM1','DataBits',7);

Data Types: double

Type of parity checking, specified as the comma-separated pair consisting of 'Parity' and none, odd, even, mark, or space.

Parity checking can detect errors of one bit only. An error in two bits might cause the data to have a seemingly valid parity, when in fact it is incorrect.

In addition to the parity bit, the serial data format consists of a start bit, between five and eight data bits, and one or two stop bits. You specify the number of data bits with the DataBits property, and the number of stop bits with the StopBits property.

You can also set the Parity property after creating the serial object using this syntax:

Example: s = serial('COM1','Parity','even');

Data Types: charstring

Number of bits used to indicate the end of a byte, specified as the comma-separated pair consisting of 'StopBits' and 1, 1.5, or 2. If StopBits is 1, one stop bit is used to indicate the end of data transmission. If StopBits is 2, two stop bits are used to indicate the end of data transmission. If StopBits is 1.5, the stop bit is transferred for 150% of the normal time used to transfer one bit.

Note

Both the computer and the peripheral device must be configured to transmit the same number of stop bits.

Summary of the possible values:

In addition to the stop bits, the serial data format consists of a start bit, between five and eight data bits, and possibly a parity bit. You specify the number of data bits with the DataBits property, and the type of parity checking with the Parity property.

You can also set the StopBits property after creating the serial object using this syntax:

Matlab Serial Port Read Example

Example: s = serial('COM1','StopBits',2);

Data Types: double

Terminator character, specified as the comma-separated pair consisting of 'Terminator' and a string. You can configure Terminator to an integer value ranging from 0 to 127, which represents the ASCII code for the character, or you can configure Terminator to the ASCII character. For example, to configure Terminator to a carriage return, specify the value to be CR or 13. To configure Terminator to a linefeed, specify the value to be LF or 10. You can also set Terminator to CR/LF or LF/CR. If Terminator is CR/LF, the terminator is a carriage return followed by a line feed. If Terminator is LF/CR, the terminator is a linefeed followed by a carriage return. Note that there are no integer equivalents for these two values.

Additionally, you can set Terminator to a 1-by-2 cell array. The first element of the cell is the read terminator and the second element of the cell array is the write terminator.

When performing a write operation using the fprintf function, all occurrences of n are replaced with the Terminator property value. Note that %sn is the default format for fprintf. A read operation with fgetl, fgets, or fscanf completes when the Terminator value is read. The terminator is ignored for binary operations.

You can also use the terminator to generate a bytes-available event when the BytesAvailableFcnMode is set to terminator.

You can also set the Terminator property after creating the serial object, using this syntax:

Example: s = serial('COM1','Terminator','CR');

Matlab Gui Serial Port Example

Data Types: charstring