CPUs
1-18
PLC S7-300, CPU Specifications CPU 312 IFM to CPU 318-2 DP
A5E00111190-01
Details
... on the communication topic are found in the STEP 7 Online Help and in the
manual Communication with SIMATIC.
... on communications SFCs/SFBs are found in the STEP 7 Online Help and in the
Standard and System functions reference manual.
Global Data Communication with S7-300 CPUs
Below you will find important features of global data communication in the S7-300.
Send/Receive Conditions
For the communication via GD circuits, you should observe the following
conditions:
Required for the GD packet transmitter is:
Reduction
ratio
Transmitter
Cycle
time
Transmitter
60 ms (CPU 318-2: 10 ms
Required for the GD packet receiver is:
Reduction
ratio
Receiver
Cycle
timer
eceiver
Reduction
ratio
Transmitter
Cycle
time
Transmitter
Non-observance of these conditions can lead to the loss of a GD packet. The
reasons for this are:
The performance capability of the smallest CPU in the GD circuit
Sending and receiving of global data is carried out asynchronously by the
sender and receiver.
Loss of global data is displayed in the status field of a GD circuit if you have
configured this with STEP 7.
Note
Note when communicating via global data: sent global data is not acknowledged
by the receiving partner!
The sender therefore receives no information on whether a receiver and which
receiver has received the sent global data.
Send Cycles for Global Data
In STEP 7 (as of Version 3.0), the following situation can arise if you set “Send
after every CPU cycle” with a short CPU cycle time (< 60 ms): the operating
system overwrites GD packets the CPU has not yet transmitted. Tip: Loss of
global data is displayed in the status field of a GD circuit if you have configured this
with STEP 7.
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