Notes on operation
4.4 Redial delay (STEP 7)
CP 1242-7
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Operating Instructions, 09/2011, C79000-G8976-C247-02
4.4
Redial delay (STEP 7)
The "Redial delay" parameter of the CP 1242-7
In "Telecontrol" mode, the redial delay is the waiting time between the connection
establishment attempts if the telecontrol server cannot be reached. It is configured in STEP
7, parameter group "Operating mode" of the CP.
A basic value is configured for the waiting time before the next connection establishment
attempt. After every 3 redial attempts, the basic value is doubled up to a maximum of 900 s.
Range of values: 10 to 600 s.
Example: The basic value 20 results in the following intervals for connection establishment
attempts:
●
three times 20 s
●
three times 40 s
●
three times 80 s
●
etc. up to max. 900 s
If a substitute telecontrol server is configured, the 4th time the CP attempts to connect to the
substitute server, in this example therefore after the following time:
●
Three times 20 s redial delay +
●
three times the connection monitoring time configured for the CP
(time until arrival of the TCP acknowledgment from the communications partner)
NOTICE
Depending on your contract, costs may result from each connection establishment
attempt.
4.5
Data management and cyclic data exchange
Data storage in the image of the CP
The process data sent by the CPU to the CP using telecontrol instructions and intended for
further transmission via GPRS is stored as an image on the CP.
When new process data is sent by the CPU to the CP, the procedure following depends on
whether the remote communications partner of the CP is an S7 station or a telecontrol
server.
Communications partner is an S7 station
After data is sent from the CPU to the CP, the CP sends the data to the remote
communications partner immediately via GPRS.
This applies both to S7 stations that can be accessed via the telecontrol server and to
stations that can be accessed directly (CP in "GPRS direct" mode).
