Tuesday, August 23, 2011

Communication PROFIBUS DP on ABB Scalable PLC

PROFIBUS DP is a high-speed, open, and broadly-used field bus. It offers master-slave and multi-master communication in the area. This field bus can consequently be utilized for AC31 and AC500 series of control system and for neutral FBP devices of field-bus through the connector of PROFIBUS-FBP.

The rule of master’s data traffic on the bus. The masters can send out data with no external request when in control of the authorization of bus access or token. The passive devices do not get any rights of bus access; they recognize messages established, or react to a query from a master. They are supported Baud rates from 9.6 kBaud to 12 MBaud. A maximum of 126 devices can be worked on the bus.

Data exchange
This is handled mainly in recurring mode between slave and master. The essential functions of communication have been identified by the basic functions of PROFIBUS DP in unity with EN 50170. Every master has full read and write admission to its allocated slaves, but only read admission to the assigned of slaves to other masters of bus. There is no straight data substitute between masters. The services of cyclical for diagnostics and parameterization between slave and master are also accessible. This is executed in parallel to the master of cyclical user data traffic.

Detailed messages of diagnostic for fast troubleshooting are displayed on the display of CPU. Additionally, the status of device is designated at the module of communication by 4 LEDs.

RTU of Modbus
The RTU of Modbus® is an open slave/master protocol, and can be simply applied on serial interfaces. Many systems automation have interfaces of Modbus RTU as standard features or optional features, and are so easily able to correspond with the AC500 through its incorporated interfaces features RS232 or RS485. The Modbus was utilized not just in manufacturing appliances, but also in systems of energy optimization, in building installations, for linking up panels of user for long-distance data transmission.

The master sends out a demand to the slave, after that gets the reaction. The interfaces of RS232 and RS485 can run concurrently as interfaces of Modbus. The operating mode of Modbus interface is put using the tool of engineering.

Data transfer
Every telegram has a CRC of 16-bit attached Maximum 115.2 kB/s. The telegrams allow process data to be read and written, either in groups or individually. The data are full in the format of RTU.

Media Transmission
One generally utilized alternative is the bus physics of RS485, terminators shielded cable, a pair of twisted.

Detailed messages of diagnostic for quick trouble-shooting are displayed on the CPU monitor.


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