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
- Raises
CanInitializationError – If the given parameters are invalid.
CanInterfaceNotImplementedError – If the serial module is not installed.
- Return type
None
- _recv_internal(timeout)[source]#
Read a message from the serial device.
- Parameters
Warning
This parameter will be ignored. The timeout value of the channel is used.
- Returns
Received message and
False(because no filtering as taken place).Warning
Flags like
is_extended_id,is_remote_frameandis_error_framewill not be set over this function, the flags in the return message are the default values.- Return type
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 |