Modbus Plus
Developed by AEG Modicon in the USA, this is becoming possibly the most widely used network in newinstallations in that country. The approach to developing this network, however, has been very different to
that of Profibus. After releasing the bus in 1989, Modicon formed a program known as the 'Modconnect
Partners' program with several leading suppliers of computer and automation products in the USA. As of
January1992, this included IBM, Uticor, US Data, Datalogic, Xycom, Hilco Technologies and Digital
Equipment Corporation (DEC). These manufacturers have all developed products or applications for direct
integration onto Modbus Plus networks.
Although not associated with the Profibus group, the characteristics of the two networks are very similar.
• network topology: linear bus with terminator, daisy chain
• medium, distances, number of stations: shielded twisted pair, ( 450 m without repeaters, 32
stations, (1800 m with repeaters, 64 stations. (Longer distances with optical fibre)
• transmission speed. 1 Mbits/s
• redundancy: second medium is optional
• addressing: 0 to 64
• station types: masters (active stations, with bus access control); (Slaves (passive stations, without
bus access control) still under development)
• bus access: hybrid, decentral/central: token passing between master stations and master-slave
between master and slave stations
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