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)[source]

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

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