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S7-300 CPU 31x -- Product information -- Background and system information
How many devices can you connect to an S7-300/S7-400 using the Modbus/TCP protocol?
Which IO controllers and IO devices support the following functions in STEP 7 (TIA Portal): IRT, prioritized startup, MRP, MRPD, PROFIenergy, Shared device, MSI/MSO, I device, Isochronous mode, System redundancy and Option handling?
What is the emergency address (emergency IP) of a CPU and when is this enabled or disabled?
All-round protection with Industrial Security - System Integrity
What are the differences between OPEN MODBUS / TCP Redundant V1 and OPEN MODBUS / TCP Redundant V2?
What is the difference between "normal routing" and data record routing?
Which SIMATIC S7-300/S7-400 modules support the NTP time-of-day message and how do you activate this kind of time synchronization?
Which manufacturer ID, in other words OUI (Organizationally Unique Identifier), does SIEMENS AG use for the MAC addresses of network-compatible devices?
What should you watch out for when using the alarm numbering procedure?
Which IO controllers and IO devices support the following functions in STEP 7 V5.5: IRT, prioritized startup, MRP, MRPD, PROFIenergy, Shared device, I device, sochronous mode, System redundancy and Option handling?
What is the maximum number of parameters that can be assigned to an FC and FB in the S7-300 CPU?
Which types of connection/protocols do the S7-300/400 CPUs and the CPs support by default?
Which PROFINET nodes support automatic commissioning (device replacement without interchangeable medium) in the case of topological configuration and device replacement without topological configuration?
Which PROFINET nodes support the extended PN diagnostics and what do you have to configure?
Why is only a warm start available for S7-300?
Which SIMATIC S7 modules support the "Direct Data Exchange" function (internode communication)?
Which entries deal with consistent data in conjunction with distributed I/O?
What properties, advantages and special features does the S7 Basis Communication offer?
What properties, advantages and special features does the global data communication offer?
What is the connection between subnet masks and IP addresses with regard to subnetting and supernetting (Classless Inter Domain Routing CIDR)?
Which modules support the S7 routing function?
How can you obtain an overview of the memory concept of SIMATIC S7-300 CPUs and C7 devices?
Retentivity behavior of S7-300 CPU 31x and complete devices C7-6xx with MMC
Status of the run-time meter after overall reset
Why does the retentivity behavior of the S7-300 CPUs and C7 devices without MMC (Micro Memory Card) influence the contents of the variables?
Local data addressing with S7-300 / S7 400
S7 300 run-time meter doesn't give any value
S7-400 CPU 41x -- Product information -- Background and system information
How many devices can you connect to an S7-300/S7-400 using the Modbus/TCP protocol?
When compiling a CFC chart, why is the error message "Time stamp conflict" displayed in connection with the Modbus/TCP FBs for S7-400 CPUs?
Which IO controllers and IO devices support the following functions in STEP 7 (TIA Portal): IRT, prioritized startup, MRP, MRPD, PROFIenergy, Shared device, MSI/MSO, I device, Isochronous mode, System redundancy and Option handling?
All-round protection with Industrial Security - System Integrity
What are the differences between OPEN MODBUS / TCP Redundant V1 and OPEN MODBUS / TCP Redundant V2?
What is the difference between "normal routing" and data record routing?
Which SIMATIC S7-300/S7-400 modules support the NTP time-of-day message and how do you activate this kind of time synchronization?
Which manufacturer ID, in other words OUI (Organizationally Unique Identifier), does SIEMENS AG use for the MAC addresses of network-compatible devices?
What should you watch out for when adding components or changing their parameters using CiR (Configuration in Run)?
Which IO controllers and IO devices support the following functions in STEP 7 V5.5: IRT, prioritized startup, MRP, MRPD, PROFIenergy, Shared device, I device, sochronous mode, System redundancy and Option handling?
Which types of connection/protocols do the S7-300/400 CPUs and the CPs support by default?
Which PROFINET nodes support automatic commissioning (device replacement without interchangeable medium) in the case of topological configuration and device replacement without topological configuration?
Behavior of the CPU after power off without back-up battery
I/O addressing with DP slaves
Which PROFINET nodes support the extended PN diagnostics and what do you have to configure?
What is the difference between a restart (warm restart), cold restart and hot restart of a S7-400 CPU?
Which SIMATIC S7 modules support the "Direct Data Exchange" function (internode communication)?
What properties, advantages and special features does the S7 Basis Communication offer?
What properties, advantages and special features does the global data communication offer?
Which entries deal with consistent data in conjunction with distributed I/O?
What is the connection between subnet masks and IP addresses with regard to subnetting and supernetting (Classless Inter Domain Routing CIDR)?
Which modules support the S7 routing function?
CPU does not work in RUN
What does "Correction factor" mean in the "Diagnostics/Clock" tab of the CPU's Properties dialog?
What is multicomputing mode and what are the differences to operating in the segmented subrack?
Differing information on the requirement of offline/ online memory
How can I get an overview of the S7-400 memory concept?
What properties, advantages and special features does the global data communication offer?
Part number:

Description:
Global data communication permits cyclic data communication between SIMATIC S7 CPUs via the MPI interface. Data communication is cyclic during updating of the process output and input images.

In addition to cyclic data transfer, it is also possible to have event-controlled data transfer in the S7-400 CPU via prepared function blocks. For this, function blocks are called in the S7 program for sending and receiving the data.

The data to be transferred is defined statically in the program and can be transferred consistently in different global data rings, i.e. defined groups of nodes that exchange global data with each other. The data can only be transferred to modules that have been parameterized in the same STEP 7 project and that use either the same communications bus (K bus) on the backplane bus or the MPI bus.

Global data communication and MPI are located as follows in the ISO-OSI reference model.

Fig. 01: ISO-OSI reference model

Global data communication services:
 
Services Description
Cyclic data transfer Cyclic data transfer covers all the configured global data rings. The data is transferred when the process image is updated.
GD_SND / GD_RCV The S7-400 sends and receives global data packages through the event-controlled data transfer via the function blocks GD_SND and GD_RCV respectively. The global data ring number and global data package number are specified on the function block.

Properties of the services:
The volume of the data to be transferred is low with a maximum of 22 bytes (S7-300 CPU) and 54 bytes (S7-400 CPU).
 
Service / Properties S7-300 S7-400
Max. data length 22 bytes 54 bytes
Max. number of GD packages for sending 4 / 8
depending on the S7-300 CPU
8 / 16
depending on the S7-400 CPU
Max. number of GD packages for receiving 4 / 8
depending on the S7-300 CPU
16 /32
depending on the S7-400 CPU
Max. number of GD rings 4 / 8
depending on the S7-300 CPU
8 / 16
depending on the S7-400 CPU
Blocks - SFC 60 "GD_SEND" / SFC 61 "GD_REC"

Advantages of global data communication:

  • Simple configuration of communication.
  • Consistent data transfer.

Disadvantages of global data communication:

  • Global data communication can be used only in homogeneous SIMATIC structures.
  • Data transfer is static.
  • Only small volumes of data can be transferred.
  • Global data communication is not acknowledged.

Notes:

  • Global data communication is not available in the S7-400H.
  • You can find general information about communication via SIMATIC S7 in Entry ID: 20982954.
  • Information on the SFCs for S7 global data communication is available in the manual "System Software for S7-300/400 System and Standard Functions" in Entry ID: 1214574.

 Entry ID:28866566   Date:2008-07-24 
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