User's Manual

Modbus telecontrol protocol26
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
Modbus - example of serial and TCP/IP telecontrol connections (multi-point/point-to-point topologies)
SINAUT
MD2
SCALANCE
X101-1LD
SCALANCE
X101-1LD
SINAUT
MD2
SINAUT
MD2
G_PCS7_XX_00273
Control center
Modbus master
SIMATIC S7-400 with
CP 443 and software library
(Modbus slave)
SIPLUS RIC bundle
with SIMATIC ET 200S
(Modbus slave)
SIPLUS RIC bundle
with SIMATIC S7-300
(Modbus slave)
Point-to-
point
Multi-point
TCP/IP to serial converter
Fiber-optic cable
TCP/IP WAN router
© Siemens AG 2011