Profibus vs Modbus-difference between Profibus and Modbus
This page compares Profibus vs Modbus and mentions difference between Profibus and Modbus.
We have seen common interface standards used for automation viz. RS232, RS422 and RS485. The profibus and Modbus are enhancement to previous interface standards. These protocols defines real time communication between masters of bus, distributed sensors and actors. They are used for low transmission volumes and low latency applications.
Note that Modbus is a protocol which defines frame structure for the messages to be transported over serial lines. RS485 defines electrical specifications. Modbus uses many different types of electrical standards including RS485. Hence Modbus communication can take place over RS232, RS422, RS485, radio, microwave, satellite etc.
| Features | Profibus | Modbus |
|---|---|---|
| Mode of operation | Operates in multi master mode using RS485. | Operates on only single master mode using ASCII/RTI. |
| Use of ethernet | Can not operate on ethernet, but profinet operates on ethernet which is not same as profibus. | Can run on ethernet using TCP/IP protocols. |
| Physical medium | twisted pair, fiber | Modbus does not define physical medium. It defines message structure which can be used over any physical medium. However Modbus RS485 is popular among all. |
| Speed of transmission | Operates at different speeds of transmission from 1.2 Kbps to 12 Mbps. | Modbus RS485 supports seed of transmissions upto 115 Kbps or upto 19.2 Kbps. |
| distance coverage | 32 stations use profibus for distances upto 1200 meters, while 2 stations communicate at speed of 500 kbps for distances upto 400 meters. Low speed transmission supports higher distances while high speed transmission supports lower distances. | Modbus RS485 cable should be less than 700 meters. |
| Number of master and slave devices | Upto 126 devices (masters and slaves) are connected on single profibus network. | Modbus master actually supports 247 slave devices. The number of slave devices including master connected on main cable are 32 due to RS485 protocol limitation. To support more than 32 repeater is used. |
| Future use | Individually use of profibus was fine, but its specialized charateristics combined with RS485 is going to be obsolete. However specialized sensor/actor fieldbus devices have increased their market penetration in automation industry now and in future. | Due to simple protocol, it has become popular as one of the main ethernet protocols in automation industry. The other older versions are RS232, RS422, RS485 etc. Devices are used on the bus with and without addresses. |
| Application | It is very robust protocol which can be used to automate entire plants. It is used where there are more points and multiple vendor equipments are to be automated. | It is very simple protocol which can be used to interface single controller in point-to-point mode of configuration. It is used for small plant automation. |
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