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Communication by the Modbus protocol

Types of Modbus communication protocols:
1st Modbus TCP/IP - classic Ethernet TCP/IP with the 10/100 Mbit/s speed rate.
2nd Modbus RTU - serial binary protocol of the Master/Slave type
3rd Modbus ASCII - serial ASCII protocol of the Master/Slave type
4th JBUS - limited set of communication messages of the Modbus RTU type
5th MODBUS PLUS - deterministic token LAN, peer-to-peer protocol, 1Mbit/s.


All protocols have common services and functions (e.g. 03-Read Holding Registers (Read Output Registers), etc.), they make use of another communication frame with various methods of addressing individual devices.

The Modbus communication protocol can be used for the following devices:
Modicon, Telemecanique, ABB AC31, Honeywell, Beckhoff, ADAM, Hypel, Tronic Control, heat meters and many others

1. Modbus TCP/IP

It is a network protocol - classic Ethernet TCP/IP with the 10/100 Mbit/s speed rate (standard net HW Ethernet card is sufficient). The communication principle (1Master x nSlave) is the same as for Modbus RTU.
For this communication in the PROMOTIC system can be used:

The data transfer into the PROMOTIC system can be also implemented over the communication OPC server that is supplied, for example, by the Schneider Electric company. (see Communication with PLC devices by the Schneider Electric company).
Note: The Schneider Electric company supplies also HW converters (bridges) with various conversions: MB/MB+, MB/Ethernet, MB+/Ethernet (all are functional in both transfer directions).

2. Modbus RTU

The serial binary communication protocol. It is the communication standard that became widely used and all series of PLC's and other device producers support it. It goes about the network protocol of the 1Master x nSlave type. The Slave devices can be 254 at the most.
For this communication in the PROMOTIC system can be used:

3. Modbus ASCII

The serial ASCII communication protocol. The protocol is similar to Modbus RTU, but the binary content is transformed to common ASCII characters. It is not used as frequently as Modbus RTU.
For this communication in the PROMOTIC system can be used:

4. JBUS

The serial JBUS protocol is the subset of the Modbus RTU protocol communication messages that makes use mostly the Modbus protocol messages for data reading/writing (messages of 1-8,11-12,15-17 types are supported). The number of Slave stations is limited to 32 at the most. The Modbus communication drivers in the PROMOTIC system promote all messages of the JBUS protocol.

5. MODBUS PLUS

It goes about the network communication protocol (deterministic token LAN). All stations are equivalent in the network (peer-to-peer access). The ModbusPlus supports in the network max. 64 stations and transfers data between them by the 1Mbit/sec speed rate.
For communication by the ModbusPlus protocol it is necessary to accommodate the PC station by the special HW network card (e.g. by the Schneider Electric company). The data transfer into the PROMOTIC system can be implemented over the communication OPC server that is supplied also by the Schneider Electric company.
PROMOTIC 9.0.27 SCADA system documentation MICROSYS, spol. s r.o.

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