Networking With Modbus/Tcp; Modbus Master With Modbus/Tcp - JUMO mTRON T Manual

5.2

Networking with Modbus/TCP

The image below provides an overview on the networking options when using the Modbus/TCP
protocol:
Modbus/TCP master
(e.g. PC/SCADA)
Each Modbus/TCP node can be uniquely addressed by an IP address. The "unit ID" (= device
address) also contained in the protocol must be the node 0xFF directly connected to the net-
work. A node, however, can virtually operate as several lower-level devices and therefore also
the central processing unit (center of image) for all connected modules. They can be accessed
with device addresses 1 to 254 (as assigned in the setup program under "H
").
MENT
5.3

Modbus master with Modbus/TCP

Up to 4 connection are possible to different Modbus/TCP devices which allow the exchange of
maximum 8 reading and 8 writing frames. A frame can be used to transmit up to 254 bytes. It
operates just like the Modbus master function via the serial interface.
 Chapter 4 "Serial transmission modes", page 49
Frames can be exchanged with 4 devices (1 to 4) on the other end using 4 sockets. The Mod-
bus device address that can be edited inside each frame mask and that is also transmitted in
the Modbus/TCP protocol can be used to address Modbus gateways and modules behind oth-
er basic modules. The latter then forwards the frame to the Modbus node behind it.
IP = x.x.x.x
Frame Frame
5 Ethernet transmission modes
Ethernet
Modbus/TCP slave
IP = x.x.x.y
(e.g. central process. unit)
Unit ID = 0xFF
System bus
Controller AI 4-ch.
Addr. = 2 Addr. = 5
Frame
Modbus/TCP slave
IP = x.x.x.z
(e.g. Modbus gateway)
Unit ID = 0xFF
Modbus network
Module 1 Module 2
Addr. = 1 Addr. = 2
Module 3
Addr. = 3
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ARDWARE ARRANGE
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