Half-Duplex Serial Port

This package uses serialport and adds half-duplex functionality (i.e. send-and-receive). It supports TypeScript.

For serial communication, one usually wants to send a command and wait for an answer. This Promise based library does exactly that.

Half-duplex means that there can always be only one party sending data. Since the commands are asynchronous and Promise based, they are protected internally with a Semaphore and not more than one caller can send and receive data at the same time.

const serial = new SerialHalfDuplex( SerialHalfDuplex.openSerialPort( '/dev/ttyUSB0' ) );
const timeoutMillis = 200;

// Send data over the serial port, wait for the response, and process it
serial.sendAndReceive( Buffer.from( 'Hello!' ), timeoutMillis )
    .then( ( answer ) => console.log( answer.toString() ) )
    .catch( ( err ) => console.error( err ) );

API

See your favourite editor’s autocomplete support for the full documentation.

new SerialHalfDuplex( port : ISerialPort, args? : SerialHalfDuplexArgs )

Constructor. args allows to configure

• delimiter which marks the end of a response
• logger like SerialHalfDuplex.consoleLogger which logs communication details, if defined

debugMode : boolean

Enable debug mode (print incoming and outgoing messages).

sendAndReceive( cmd : Buffer, timeout : number ) : Promise<Buffer>

Send a command and wait for an answer.

The timeout is in milliseconds. It is required because serial communication does not specify a request/response protocol and we just assume the client will respond within a defined amount of time (but it might not reply at all, for example because it is disconnected).

sendAndReceiveMany( …, expectedLines : number ) : Promise<Buffer[]>

Send a command and wait for multiple answers.

The command resolves when at least one line is returned within the timeout.

Waiting for multiple lines is useful in cases where a device returns multiple lines to one command. For example, the Acer beamer H5382BD replies with *001\rLAMP 0\r when querying the lamp state.

send( cmd : Buffer ) : Promise<void>

Simply send a command without waiting for an answer.

Testing serial communication

Testing serial ports without the real target device can be done e.g.

• by programming an Arduino to behave like the real device
• with socat and minicom

Socat can open a pair of serial ports.

socat -d -d pty,raw,echo=0 pty,raw,echo=0
2019/12/22 09:57:26 socat[12018] N PTY is /dev/pts/3
2019/12/22 09:57:26 socat[12018] N PTY is /dev/pts/4
2019/12/22 09:57:26 socat[12018] N starting data transfer loop with FDs [5,5] and [7,7]

Minicom can then connect to one end and the application to the other end. Do not forget to enable echo (Ctrl+A E) and disable hardware flow control (Ctrl+A O → Serial port setup → Hardware Flow Control).

minicom -b 9600 -o -D /dev/pts/4

Be aware that minicom only sends carriage return \r, but not new lines \n after commands. It therefore cannot be used for debugging.

To analyse the exact data which is sent through minicom, attach strace to the minicom process ID. Note that also stdin/stdout data is shown with file descriptors 0 and 1.

strace -p PID -e read,write

Changelog

vNext

v4.0.1 (2024-02-27)

• Fixed: openSerialPort() optional arguments can be partial
• Fixed: findSuitablePort() predicate is now actually used

v4.0.0 (2024-02-27)

This version updates from SerialPort 9 to 12 and improves logging.

• Changed: Better error message in case of timeout
• Changed: Log callback count when receiving spontaneous message
• Changed: Update serialport to version 10
• Breaking: Node.js 14 or newer is required.

v3.1.0 (2022-02-08)

• Added: The SerialPort port object is now exposed.
• Changed: Answer timeouts now reject with a TimeoutError

v3.0.0 (2021-03-29)

• Changed: Constructor now takes a logger for debugging instead of a boolean flag. This does not force the usage of console anymore and allows customising output.

v2.1.0 (2021-03-03)

• Changed: SerialHalfDuplex.findSuitablePort() now accepts a predicate which determines if a port is suitable, instead of only listing CP210x UART bridges. (This is still the default filter, so the change is backwards compatible.)
• Changed: Dependencies updated

v2.0.1 (2020-06-09)

• Changed: Updated packages (fixes bl vulnerability)
• Breaking: Updated serialport to v9 to support Node.js 14. This requires Node.js > 8.

v1.3.1 (2019-12-22)

• Changed: Documentation updated

v1.3.0 (2019-12-19)

• Added: SerialHalfDuplex.sendAndReceiveMany. Receives more than one line.

v1.2.0 (2019-11-27)

• Changed: SerialHalfDuplex accepts a configuration object to configure the response delimiter
• Changed: SerialHalfDuplex.openSerialPort now accepts arguments for serial port configuration.