Communication
3.2 Communication services
CPU 31xC and CPU 31x, Technical Data
Manual, 01/2006 Edition, A5E00105475-06
3-9
Table 3-3 Client and server in S7 communication, using connections with unilateral / bilateral
configuration
CPU Use in server mode for
connections with unilateral
configuration
Use in server mode for
connections with bilateral
configuration
Use as client
31xC >= V1.0.0 Generally possible on
MPI/DP interface without
configuration of user
interface
Only possible with CP
and loadable FBs.
Only possible with CP
and loadable FBs.
31x >= V2.0.0 Generally possible on
MPI/DP interface without
configuration of user
interface
Only possible with CP
and loadable FBs.
Only possible with CP
and loadable FBs.
31x >= V2.2.0 Generally possible on
MPI/DP/PN interface
without configuration of user
interface
• Possible on PN
interface with
loadable FBs
or
• with CP and loadable
FBs.
• Possible on PN
interface with
loadable FBs
or
• with CP and loadable
FBs.
The user interface is implemented using standard function modules (FBs) from the standard
library of STEP 7, under communication blocks.
Reference
For further information on communication, refer to the
Communication with SIMATIC
manual.
3.2.6 Global data communication (MPI only)
Properties
Global data communication is used for cyclic exchange of global data via MPI subnets (for
example, I, Q, M) between SIMATIC S7 CPUs (data exchange without acknowledgement).
One CPU broadcasts its data to all other CPUs on the MPI subnet. This function is
integrated in the CPU operating system.
Reduction ratio
The reduction ratio specifies the cyclic intervals for GD communication. You can set the
reduction ratio when you configure global data communication in STEP 7. For example, if
you set a reduction ratio of 7, global data are transferred only with every 7th cycle. This
reduces CPU load.
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