Connection
to S7-300 cannot be established
If the S7 driver cannot establish a connection
to the PLC, but the PLC is in the network and can be reached via
a PING command, perform the following
steps (appears often in a redundant WinCC OA
system):
Check the maximum number
of allowed connections in the STEP7 environment (check also
the number of reserved connections from the maximum number).
The S7 driver in WinCC OA does not use
the connections for the "S7
basis communication". For example:
A S7-314 has 12 connections as a maximum. Reserved are: 1 connection
for PG communication, 1 connection for OP communication and
8 connections for "S7 basis
communication". I.e. only 2 for "Other
connection" remain.
If you need more connections
for "Other connection",
you have to reduce the 8 connections for basis communication.
As a result the driver has more connection possibilities without
fallback to PG or OP communication.
NOTE
In case of high data volume (a number of telegrams
that could not be sent) and in case of a Simatic PLC, it is recommended
to increase the value of the parameter "% of process used
for communication" (defines how much of the CPU time is used
for the communication) in the hardware configuration of Simatic
CPU.
Slow communication to S7 300 PLCs
A bad data throughput can be the causal by using
the PLC of the type S7 315-2 PN/DP, if in the PLC program not
enough big FCs are passed by OB1. Thus the PLC has not much time
to handle the communication. A PLC of the same type and similar
loop time where are running a lot small FCs is communicating faster
by the factor of 5-10.
The adapting of the PLC program with the few FCs
in this order that the FCs are triggered by call up alarms (OB35)
and not by OB1 may decrease the factor of the polling rate by
10.
This behavior has been to date observed only with
CPUs with an onboard PN interface. That means that it is not sure
that this problem is not the same using separate TCP/IP CPs.
It should be considered that there are differences
in the communication handling in S7-300 and S7-400:
Configuration of a redundant S7400H device
Configuration of the automatic switch-over between
device 1 and device 2 based on the PLC Tag, when the active PLC
is changed to STOP state and thus the TCP connection to WinCC OA persists.
The PLC
Tag, which indicates whether device 1 ("0")
or device 2 ("1) is active, must be available. Additionally,
the option "Automatic-H"
has to be selected. This settings have to be set during the
configuration of the redundant devices (see Device
Configuration).
Set the config
entry ReadOpState
to 5 seconds or lower (see Possible
config entries of the S7 driver).
Set the config
entry AliveInterval
to >= as the max. needed polling time of a block and >=
5 seconds.
Communication with ET200 S
To enable the communication between
the S7 driver and a ET200 S a Interfacemodul IM151-8 PN/DP CPU
is necessary. With this, the ET200 S can be configured as a S7
300.
Step7 Project Path
If the path to the Step7 project,
which is used for S7 Alarming inside a WinCC OA
project, changes, the link inside the WinCC OA
project must be updated. To update the path, the value of the
element ProjectName of the internal data point S7_Conn
must be deleted manually. Afterwards the Step7 project must be
imported again (see alarm
configuration) to continue using the S7 Alarming. |