Difference between revisions of "Modbus"
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Revision as of 06:04, 31 July 2013
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.
<a class="image" href="http://www.proview.se/wiki/index.php?title=File:Function-codes-modbus.png"><img src="http://www.proview.se/wiki/images/7/7c/Function-codes-modbus.png" alt="Function-codes-modbus.png" width="818" height="535" /></a>
