MODBUS has become a widely used fieldbus throughout in the world since its introduction in 1979. It is a serial based communication protocol and has two serial variants – MODBUS RTU and MODBUS ASCII. It is often used in conjunction with another fieldbuses via fieldbus gateways, but is ideal in networking controllers, sensors, actuators and binary terminal devices in the automation environment in a cost effective manner.
The course begins with an introduction to what MODBUS is and its history. We see where Modbus fits in as a digital communications system and what its advantages are over traditional analogue systems.
As Modbus can be implemented over multiple transmission mediums we learn about the physics behind its implementation over the copper wire medium in terms of the following subjects:
- Electromagnetic Interference
- Electrostatic Interference
- Signal Attenuation
We look at Serial Modbus over RS485, RS232 and RS422 and also wireless and remote monitoring (GPRS) solutions (also for Modbus TCP). The course then covers the Modbus protocol versions in more detail:
- Modbus RTU
- Mobus ASCII
- Modbus TCP
We look at where these versions fit into the OSI model, their frame formats and how to decode Modbus messages. It is also explained how Modbus operates as a Master/Slave protocol.
Finally the course takes a practical look at memory access, how data is stored, data types, "Endianess", bit and byte significance and bit masking.
Each trainee will receive both theoretical and hands-on-practical training with a number of tutorials. In the practical’s the trainees will decode messages, use a Modbus simulator to manipulate register data, read in real values from temperature and proximity sensors, control a drive and transmit data wirelessly using Modbus TCP.