Modbus

Modbus is a serial communications protocol published by Modicon in 1979.

Simple and robust, it has since become a <em><a class="new" title="De facto (page does not exist)" href="http://www.proview.se/wiki/index.php?title=De_facto&action=edit&redlink=1">de facto</a></em> <a class="new" title="Standardization (page does not exist)" href="http://www.proview.se/wiki/index.php?title=Standardization&action=edit&redlink=1">standard</a> communication protocol, and it is now amongst the most commonly available means of connecting industrial devices.

The main reasons for the extensive use of Modbus in the industrial environment are:

It has been developed with industrial applications in mind
It is openly published and royalty-free
It is easy to deploy and maintain
It moves raw bits or words without placing many restrictions on vendors

Modbus allows for communication between many (approximately 240) devices connected to the same network, for example a system that measures temperature and humidity and communicates the results to a computer. Modbus is often used to connect a supervisory computer with a <a class="new" title="Remote terminal unit (page does not exist)" href="http://www.proview.se/wiki/index.php?title=Remote_terminal_unit&action=edit&redlink=1">remote terminal unit</a> (RTU) in supervisory control and data acquisition SCADA systems. Many of the data types are named from its use in driving relays: a single-bit physical output is called a coil, and a single-bit physical input is called a discrete input or a contact.

The development and update of Modbus protocols are managed by the <a class="external text" rel="nofollow" href="http://www.modbus.com/">Modbus Organization</a>, formed of independent users and suppliers of Modbus compliant devices.

Modbus

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