Technical data

8.1.1 FDL Services implemented in a CP 5430 TF/CP 5431 FMS for
Data Transmission
The layer 2 firmware of the CP 5430 TF/CP 5431 FMS provides various
services for reliable data transmission which can be used in the control
program. In concrete terms this means that the control program can request
layer 2 data transmission services and can evaluate confirmations (and
error messages) made available by this layer. You must also evaluate
indications from layer 2 when a frame is received by the CP.
SDA (Send
Data with
Acknowledge):
Data is sent to the remote station and this
acknowledges reception.
SDN (Send
Data with No
Acknowledge):
Data is sent to the remote station but this does not
acknowledge reception.
SRD (Send and
Request Data):
Data is sent to the remote station and at the same time
data is requested from it. The requested data must
already be prepared by the remote station in a transfer
buffer.
RPL_UPD_S
(RePLy-
UPDate-Single):
With this service the transfer buffer is filled with data to
be fetched by the communications partner using the
SRD service. Once the data have been fetched, the
buffer is empty.
RPL_UPD_M
(RePLy-UPDate
-Multiple):
With this service the transfer buffer is filled with data to
be fetched by the communications partner using the
SRD service. The data are not deleted after they have
been fetched (they remain available until they are
overwritten).
You use these services provided by the layer 2 firmware of the CP 5430
TF/CP 5431 FMS in the STEP 5 control program by programming handling
block calls.
B8976060/02 Free Layer 2 Communication
8 - 3 Volume 1