Overview Global data communication is a simple communication service that is
integral to the operating system of the S7-300/400 CPUs.
Features GD communication facilitates the cyclic exchange of global data, such as inputs, outputs, bit memories and areas in data blocks, between CPUs via the MPI interface (without using blocks). Cyclic data transfer takes place with the normal transfer of the process image.
The response time is dependent on the cycle of the user program and its value is a fraction of this cycle time (GD reduction factor).
Transmission Reliability
This technique is a broadcast technique; therefore, there is no guarantee for data security.
Integration in STEP 7
Global data communication is configured with STEP 7 via a global data table. All S7-300/400 CPUs must be located in the same STEP 7 project.
Communication Services
2.9 AS-i Services
Overview AS-i services facilitate direct communication with decentralized actuators and sensors. From the control program, they are addressed as if they were distributed I/O.
The AS-i specification has been submitted in the form of a prototype standard to the IEC and EN.
Sensors and actuators that comply with this specification can be con- nected.
Features The sensors and actuators are addressed in the central controller or ex- pansion unit in the same manner as any other I/O. This means that the sensors and actuators can be directly addressed with instructions or they can be accessed via process image transfer.
• Power is supplied and data is transferred on the same cable.
• For each AS-i slave station, 4 sensors and actuators can be con- nected.
• Up to 4 input bits and 4 output bits are available per slave station.
• Transmission takes place at a fixed cycle time of up to 5 ms.
• The response time is <= 5 ms.
The AS-i interface is available as a separate interface (CP) for SIMATIC S7-200/300 and M7 300.
Transmission Reliability
A high degree of data security is achieved due to automatic repetition and additional checking mechanisms (parity bit and a special signal shape).
Integration in STEP 7
As far as configuration is concerned, the CP is simply integrated during hardware configuration.
Communication Networks
Communication with SIMATIC
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3 Communication Networks
Overview In this Chapter, you will become familiar with the communication networks that are available for SIMATIC. You will learn which protocols are realized in which network and which SIMATIC products are offered for these communication networks. On the basis of this information, you will be able to select your own communication network.
Chapter Overview In Section You will find On page
3.1 Overview 3-2
3.2 Multipoint Interface (MPI) 3-5
3.3 PROFIBUS 3-7
3.4 Industrial Ethernet 3-12
3.5 Point-to-Point Link 3-14
Communication Networks
3.1 Overview
Subnets in SIMATIC
SIMATIC offers the following subnets which meet the requirements of the different automation system levels (management, cell, field and actua- tor/sensor level):
MPI The MPI subnet meets the requirements of the field level and cell level with low coverage. MPI is a multipoint interface in SIMATIC S7/M7 and C7 systems. It is designed as a programming device interface and is intended for networking a small number of CPUs for the purpose of exchanging small volumes of data.
PROFIBUS PROFIBUS is the network for the cell and field level in the open, multi- vendor SIMATIC communication system.
Two versions of PROFIBUS are offered:
• PROFIBUS DP, the fieldbus for high-speed, cyclic transfer of small volumes of data
• PROFIBUS, in the cell, for the high-speed exchange of medium- sized quantities of data with communication partners that have equal rights
Industrial Ethernet Industrial Ethernet is the network for the management and cell level in the open, multi-vendor SIMATIC communication system. Industrial Ethernet is suitable for the high-speed exchange of large quantities of data and facili- tates communication between one site and another via gateways.
Point-to-Point Link
A point-to-point link is not technically a subnet. In SIMATIC, this link is implemented via point-to-point communication processors (CP), whereby two stations are linked together.
AS-Interface The AS-Interface or actuator/sensor interface is a subnet system for the lowest process level in automation systems. It is specially designed for the interconnection of binary sensors and actuators. The data volume is lim- ited to 4 bits per slave station.
Communication Networks
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Access Technique The access technique specifies how and when a station can send its data on the subnet. In the event of simultaneous requests to send from different stations, it controls the access authorization. The following types of access techniques exist:
• CSMA/CD (carrier sense multiple access / collision detection)
• Token passing
• Master/slave
The access techniques are described in detail in the sections describing the relevant subnets.
Max. Length of Network
This is the greatest distance between two stations of a subnet. A subnet can comprise one or more segments (bus segments). Bus segments can be connected via segment couplers such as repeaters or bridges.
Transfer Medium The transfer medium is the bus cable via which data is transferred. A distinction is usually made between copper and fiber-optic cables.
• Copper: 2-core cable, coaxial cable, twisted pair
Communication Networks
Technical Data The following table provides an overview of the subnets.
Features MPI PROFIBUS Industrial
Ethernet
AS-Interface
Standards SIEMENS pro-
cedure PROFIBUS to EN 50170 Volume 2 Ethernet to IEEE 802.3 AS-i specification to IEC TG 17B Access technique Token passing Token passing
with subordinate master/slave
CSMA/CD Master/slave
Transmission rate 187.5 Kbit/s 9.6 Kbit/s - 12 Mbit/s
10 Mbit/s 167 Kbit/s
Transfer medium Copper:
Shielded 2-core cable Fiber-optic: Glass or plastic fiber-optic cable Copper: Shielded 2-core cable Fiber-optic: Glass or plastic fiber-optic cable Copper: Double-shielded coaxial cable or Industrial Twisted Pair Fiber-optic: Glass fiber-optic cables Copper: Unshielded 2-core cable Max. no. of stations 32 127 > 1000 32 Max. length of network 50 m (expandable us- ing RS485 re- peaters or opti- cal link modules)
Copper: Approx. 10 km 1) Fiber-optic: over 100 km 2) Copper: 1.5 km Fiber-optic: 4.5 km
Cable length max. 300 m
Topology Line, tree,
ring, star Line, tree, ring, star Line, tree, ring, star Line, tree
Services S7 functions, GD S7 functions, FDL, FMS, DP S7 functions, ISO transport, ISO-on-TCP AS-i functions Automation system level
Cell and field level
Cell and field level
Management and cell level
Actuator/sensor level
Communication Networks
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