About mbusd

mbusd is open-source Modbus TCP to Modbus RTU (RS-232/485) gateway.

Features:

• Small footprint - suitable to run on embedded devices and SBCs like Raspberry Pi
• Multi-master - multiple TCP masters can access slave devices in RTU network using same gateway
• Robustness - can retry requests with mismatched response CRC
• Flexible RTU modes - speed/parity/stop-bits/timeouts can be configured for RTU network
• Support for both of automatic and manual (using RTS bit) direction control types for RS-485 transceivers

Supported function codes:

• 01: Read coil status
• 02: Read input status
• 03: Read holding registers
• 04: Read input registers
• 05: Force single coil
• 06: Preset single register
• 07: Read exception status
• 15: Force multiple coils
• 16: Preset multiple registers

Please note all other function codes (including vendor-specific extensions) are supported on a "best-effort" basis and most likely will fail.

Configuring and compilation:

$ git clone https://github.com/3cky/mbusd.git mbusd.git
$ cd mbusd.git
$ ./configure
$ make
# make install
$ make clean

Usage:

   mbusd [-h] [-d] [-t] [-v level] [-L logfile] [-p device] [-s speed] [-m mode] \
   	       	[-P port] [-C maxconn] [-N retries] [-R pause] [-W wait] [-T timeout]

   -h     Usage help.
   -d     Instruct mbusd not to fork itself (non-daemonize).
   -t     Enable RTS RS-485 data direction control (if not disabled while compile).
   -y file
          Enable RS-485 direction data direction control by writing '1' to file
          for transmitter enable and '0' to file for transmitter disable
   -Y file
          Enable RS-485 direction data direction control by writing '0' to file
          for transmitter enable and '1' to file for transmitter disable
   -v level
          Specifies  log  verbosity level (0 for errors only, 1 for warnings
          and 2 for also information messages.) If mbusd was compiled in debug mode,
          valid log levels are up to 9, where log levels above 2 forces
          logging of information about additional internal events.
   -L logfile
          Specifies log file name ('-' for logging to STDOUT only, default is /var/log/mbusd.log).
   -p device
          Specifies serial port device name.
   -s speed
          Specifies serial port speed.
   -m mode
          Specifies serial port mode (like 8N1).
   -P port
          Specifies TCP port number (default 502).
   -C maxconn
          Specifies maximum number of simultaneous TCP connections.
   -N retries
          Specifies maximum number of request retries (0 disables retries).
   -R pause
          Specifies pause between requests in milliseconds.
   -W wait
          Specifies response wait time in milliseconds.
   -T timeout
          Specifies connection timeout value in seconds (0 disables timeout).

Please note running mbusd on default Modbus TCP port (502) requires root privileges!

systemd:

mbusd has systemd support. The build system detects whether the system has systemd after which sudo make install installs the mbusd@.service file on systems with systemd active. The mbusd service can be started via:

# systemctl start mbusd@<serial port>.service

where <serial port> is serial port device name (like ttyUSB0).

To see the mbusd service status:

# systemctl status mbusd@<serial port>.service

To monitor the mbusd service:

# journalctl -u mbusd@<serial port>.service -f -n 10

To start the mbusd service on system boot:

# systemctl enable mbusd@<serial port>.service

Please check systemd documentation for other usefull systemd commands

The checked in mbusd@.service starts mbusd equivalent to the following command:

# $PREFIX/bin/mbusd -p /dev/<serial port> -s 9600 -m 8N1 -P 502 -d -v2

Feel free to modify the service file locally with your own desired configuration.

Reporting bugs:

Please file issue with attached debug log in verbose (-v9) mode, i.e.:

   # mbusd -L/tmp/mbusd.log -p /dev/ttyUSB0 -s 9600 -P 502 -d -v9

Unless you were prompted so or there is another pertinent reason (e.g. GitHub fails to accept the bug report), please do not send bug reports via personal email.

Contributing:

1. Fork it and clone forked repository
2. Create your feature branch (git checkout -b my-new-feature)
3. Make your changes
4. Commit your changes (git commit -am 'Add some feature')
5. Push to the branch (git push origin my-new-feature)
6. Create new Pull Request

Author:

Victor Antonovich (v.antonovich@gmail.com)

Credits:

Andrew Denysenko (nitr0@seti.kr.ua):

• RTS RS-485 data direction control
• RTU response receiving by length

James Jarvis (jj@aprsworld.com):

• file based RS-485 data direction control

License:

This project is distributed under the BSD license. See the LICENSE file for the full license text.