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Victor Antonovich
© 2002-2003

MODBUS/TCP to MODBUS/RTU gateway server

This is free MODBUS/TCP to MODBUS/RTU gateway server (mbusd) and development support library (libmbus).


MODBUS protocol is widely used in automation and industrial control applications (see links for the further information), but most products are commercial and their sources are closed. mbusd server was written from scratch, uses FSM for effective client queries processing and seems to be very portable (i.e., may be used in embedded applications under uCLinux in the future).

Current platforms tested are FreeBSD 4, Red Hat Linux 8.0 and Win32 (under Cygwin environment).

Here is the project page on SourceForge and here is the download area, the CVS repository and the mailing lists. Below is a more detailed description of the subprojects.


The mbusd gateway server allows MODBUS/TCP based controllers and applications to communicate and interoperate with serial MODBUS RTUs. The MODBUS standard protocol is an asynchronous protocol designed to connect directly to computer asynchronous ports. MODBUS/TCP is MODBUS extension to operate over IP links using the TCP/IP protocol suite. mbusd gateway server converts between the MODBUS/TCP protocol and MODBUS/RTU protocols transparently.

Please note that currently mbusd can't operate with RS-232/RS-485 converters with direction switching by RTS pin. Use converters with automatic data direction control (i.e. Moxa Transio series).


The libmbus development support library contain limited set of MODBUS/TCP query functions and connection management routines. See libmbus(3) and libmbus_cmd(3) man pages for further details.


Both mbusd and libmbus are distributed under BSD license, as noted in each source file.

Mailing list

Whe have a mailing list for discussions about the mbusd and libmbus. You can subscribe to mbus-users on this page.

Help Wanted

Interested in participating in a open source project? We have some interesting stuff to work on. See here for more infos.

Comments and bug reports are appreciated. If you can test this software, let us know of success or failure (bugs). When you want to extend the library or add new features to server, let us know. This is an open source project where everyone can make the product better.

This project is hosted on SourceForge.net, the place to search open source:
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This page is located at http://mbus.sourceforge.net