NETLink
®
Switch
20
Some older Siemens CPUs do not support the auto baud function
on the MPI. PPI systems do not usually support this function ei-
ther. In such cases, the network-related parameters should be
adapted manually.
The transmission speed and the HSA of the PLC being addressed
must be known and identical to all connected bus nodes.
It is also possible that the auto baud function may not function
reliably at transmission rates slower than or equal to 19.2 Kbps or
with increased use of communication via global data exchange,
because the relevant frame is transmitted more irregularly by the
CPUs. In such cases it may be advantageous to assign the bus pa-
rameters manually.
5.1.2
PROFIBUS configuration
Basically, the same applies to PROFIBUS configuration as to MPI
configuration. However, the network-related parameters are more
extensive.
In addition to the parameters transmission rate and highest sta-
tion address mentioned in Section
5.1.1, PROFIBUS also has pa-
rameter field for selecting the bus profile and bus parameters.
If the NETLink
®
Switch is the only active station on the
PROFIBUS, it operates in so-called single-master mode, i.e. it gen-
erates the token cycle with the set bus parameters.
If the bus speed on the PROFIBUS is set to a value less than 187.5
Kbps, please remember that it may take up to half a minute for
the bus parameters to be recognized.