CAN over Serial

A text based interface. For example use over serial ports like /dev/ttyS1 or /dev/ttyUSB0 on Linux machines or COM1 on Windows. Remote ports can be also used via a special URL. Both raw TCP sockets as also RFC2217 ports are supported: socket://192.168.254.254:5000 or rfc2217://192.168.254.254:5000. In addition a virtual loopback can be used via loop:// URL. The interface is a simple implementation that has been used for recording CAN traces.

Note

The properties extended_id, is_remote_frame and is_error_frame from the class:~can.Message are not in use. This interface will not send or receive flags for this properties.

Bus

class can.interfaces.serial.serial_can.SerialBus(channel, baudrate=115200, timeout=0.1, rtscts=False, *args, **kwargs)

Enable basic can communication over a serial device.

Note

See _recv_internal() for some special semantics.

Parameters

• channel (str) – The serial device to open. For example “/dev/ttyS1” or “/dev/ttyUSB0” on Linux or “COM1” on Windows systems.

• baudrate (int) –

  Baud rate of the serial device in bit/s (default 115200).

  Warning

  Some serial port implementations don’t care about the baudrate.

• timeout (float) – Timeout for the serial device in seconds (default 0.1).

• rtscts (bool) – turn hardware handshake (RTS/CTS) on and off

Raises

• can.CanInitializationError – If the given parameters are invalid.

• can.CanInterfaceNotImplementedError – If the serial module is not installed.

Internals

The frames that will be sent and received over the serial interface consist of six parts. The start and the stop byte for the frame, the timestamp, DLC, arbitration ID and the payload. The payload has a variable length of between 0 and 8 bytes, the other parts are fixed. Both, the timestamp and the arbitration ID will be interpreted as 4 byte unsigned integers. The DLC is also an unsigned integer with a length of 1 byte.

Serial frame format

	Start of frame	Timestamp		DLC	Arbitration ID	Payload	End of frame
Length (Byte)	1	4		1	4	0 - 8	1
Data type	Byte	Unsigned 4 byte integer		Unsigned 1 byte integer	Unsigned 4 byte integer	Byte	Byte
Byte order	-	Little-Endian		Little-Endian	Little-Endian	-	-
Description	Must be 0xAA	Usually s, ms or µs since start of the device		Length in byte of the payload	-	-	Must be 0xBB

Examples of serial frames

CAN message with 8 byte payload

CAN message
Arbitration ID	Payload
1	0x11 0x22 0x33 0x44 0x55 0x66 0x77 0x88

Serial frame
Start of frame	Timestamp	DLC	Arbitration ID	Payload	End of frame
0xAA	0x66 0x73 0x00 0x00	0x08	0x01 0x00 0x00 0x00	0x11 0x22 0x33 0x44 0x55 0x66 0x77 0x88	0xBB

CAN message with 1 byte payload

CAN message
Arbitration ID	Payload
1	0x11

Serial frame
Start of frame	Timestamp	DLC	Arbitration ID	Payload	End of frame
0xAA	0x66 0x73 0x00 0x00	0x01	0x01 0x00 0x00 0x00	0x11	0xBB

CAN message with 0 byte payload

CAN message
Arbitration ID	Payload
1	None

Serial frame
Start of frame	Timestamp	DLC	Arbitration ID	End of frame
0xAA	0x66 0x73 0x00 0x00	0x00	0x01 0x00 0x00 0x00	0xBB