mbusd is open-source Modbus TCP to Modbus RTU (RS-232/485) gateway.
- 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.
$ git clone https://github.com/3cky/mbusd.git mbusd.git $ cd mbusd.git $ mkdir -p build && cd build $ cmake -DCMAKE_INSTALL_PREFIX=/usr .. $ make $ sudo make install
Compile time options
can be altered in many ways, e.g. by using the following tools in the
- ccmake - usually in the package cmake-curses-gui
- cmake-gui - usually in the package cmake-qt-gui
mbusd [-h] [-d] [-L logfile] [-v level] [-c cfgfile] [-p device] [-s speed] [-m mode] [-t] [-y file] [-Y file] [-P port] [-C maxconn] [-N retries] [-R pause] [-W wait] [-T timeout] -h Usage help. -d Instruct mbusd not to fork itself (non-daemonize). -L logfile Specifies log file name ('-' for logging to STDOUT only, default is /var/log/mbusd.log). -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. -c cfgfile Read configuration from cfgfile. -p device Specifies serial port device name. -s speed Specifies serial port speed. -m mode Specifies serial port mode (like 8N1). -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 -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!
mbusd can read the configuration from a file specified by
-c command line flag.
Please see example configuration file
for complete list of available configuration options.
mbusd has systemd support.
The build system detects whether the system has systemd after which
sudo make install
mbusd@.service file on systems with systemd active.
The mbusd service can be started via:
# systemctl start mbusd@<serial port>.service
<serial port> is serial port device name (like
mbusd started by systemd will read its configuration from file named
This way it's possible to run multiple mbusd instances with different configurations.
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
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.
- Fork it and clone forked repository
- Create your feature branch (
git checkout -b my-new-feature)
- Make your changes
- Commit your changes (
git commit -am 'Add some feature')
- Push to the branch (
git push origin my-new-feature)
- Create new Pull Request
Victor Antonovich (firstname.lastname@example.org)
Andrew Denysenko (email@example.com):
- RTS RS-485 data direction control
- RTU response receiving by length
James Jarvis (firstname.lastname@example.org):
- file based RS-485 data direction control
Luuk Loeffen (email@example.com):
- systemd support
Nick Mayerhofer (firstname.lastname@example.org):
- CMake build system
This project is distributed under the BSD license. See the LICENSE file for the full license text.