Modbus telecontrol protocol

The Modbus telecommunication protocol is suitable for the integration of existing units with a Modbus infrastructure into the SIMATIC PCS 7 process control system.

Telecontrol communication for control and monitoring of widely distributed outstations (RTUs) from a control center in SIMATIC PCS 7 is possible with this protocol via both serial and TCP/IP communication links.

The control center, represented by the SIMATIC PCS 7 Operator System with SIMATIC PCS 7 TeleControl, is the Modbus master. SIMATIC S7 controllers (SIMATIC ET 200S with integral CPU, SIMATIC S7-300/S7-300F, and SIMATIC S7-400/S7-400F) as well as third-party RTUs with a suitable Modbus interface can be used as outstations (Modbus slaves).

The SIPLUS RIC range includes low-cost bundles for out- stations with Modbus telecontrol protocol (serial or TCP/IP), based on SIMATIC ET 200S with integral CPU and SIMATIC

S7-300. These usually comprise:

•CPU

•Interface/communication module (if necessary)

•Memory card

•CD with library and registration code.

In addition, further material is required to establish

the telecommunication links, e.g. TCP/IP converters – serial, dedicated line modems, media converters, TCP/IP routers, switches, cables etc.

The Modbus telecontrol protocol can be used to implement telecontrol networks based on point-to-point and multi-point topologies, both serial and TCP/IP. The following media can be used for this:

Classic WAN media

•Dedicated line via modem, e.g. SINAUT MD2

•Dedicated line over fiber-optic cables

•Private wireless networks

TCP/IP-based WAN media

•Ethernet networks, e.g. SCALANCE X with fiber-optic cables

•Industrial Wireless LAN with SCALANCE W

•Public networks and the Internet using DSL and/or GPRS

To permit redundant data transmission, outstations can be connected to the control center in the SIMATIC PCS 7 process control system over two paths. Two operating modes are available:

•Load sharing: parallel utilization of both paths

•Master/standby: only one path is active, the other is passive

TCP/IP WAN router

SCALANCE

X101-1LD

Fiber-optic cable

SCALANCE

X101-1LD

SIMATIC S7-400 with CP 443 and software library (Modbus slave)

Control center

Modbus master

TCP/IP to serial converter

SINAUT

MD2

SINAUT

MD2

SIPLUS RIC bundle	SIPLUS RIC bundle
with SIMATIC ET 200S	with SIMATIC S7-300
(Modbus slave)	(Modbus slave)

Point-to- point

Multi-point

G_PCS7_XX_00273

Modbus - example of serial and TCP/IP telecontrol connections (multi-point/point-to-point topologies)

Siemens SIMATICS PCS7 brochure Modbus telecontrol protocol