General Information On Communication - Siemens SIMATIC S7-400H Manual

Communication Functions

General Information on Communication

Reduce the amount of the communication jobs per second as much as possible.
Use the maximum user data length for the communication jobs by grouping some
variables and data areas in one read job.
Each job requires a processing period, its status should therefore not be checked
until the expiration of this period.
A free tool for estimating the processing time is available for download at:
http://www4.ad.siemens.de/view/cs/de/1651770, article ID 1651770
Call the communication jobs in a way that allows event–controlled data transfer.
You can only continue to check the result of the data transfer until the completion
of the job.
Call the communication blocks at time intervals and in slow cycles to distribute the
communication load evenly.
If no user data is to be transferred, you can skip the block call with a conditional
jump.
If you use S7 communication functions instead of instead of S5 compatible
commnunication functions, you will get a considerably higher communication
performance with the S7 components.
Use S5 compatible communication (FB "AG_SEND", FB "AG_RECV", AP_RED)
only when S7 components are not to communicate with non–S7 components
because S5 compatible communication functions (FB "AG_SEND", FB
"AG_RECV", AP_RED) produce a substantially higher communication load.
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Automation System S7-400H Fault-tolerant Systems
A5E00068197-07