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:
If PROMOTIC application has to be
Master:
If PROMOTIC application has to be
Slave:
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:
If PROMOTIC application has to be
Master:
If PROMOTIC application has to be
Slave:
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.