Technical data

The layer 2 firmware of the CP provides various services for reliable data
transmission which you can use in the control program. In concrete terms,
this means that you request layer 2 services for data transfer and evaluate
confirmations (including error messages) made available by this layer in the
control program. You must also evaluate layer 2 indications when a frame is
received by the CP.
The FDL services specified in PROFIBUS (DIN 19245/1) and implemented
in the CP for data transmission are as follows:
➣
FDL_DATA.-req/-ind/-conf (SDN service)
➣
FDL_DATA_ACK.-req/-ind/-conf (SDA service)
➣
FDL_DATA_REPLY.-req/-ind/-conf (SRD service)
➣
FDL_SEND_UPDATE.-req/-ind/-conf (RPL_UPD_S)
➣
FDL_REPLY_UPDATE.-req/-ind/-conf (RPL_UPD_M).
You use these services provided by the layer 2 firmware of the CP in your
STEP 5 control program by calling handling blocks which refer to job
buffers. The job buffer (PDU) must be completed by the user. The first 8
bytes ("header") of the job buffer to be transferred contain control
information for the layer 2 firmware. The receiver can evaluate the first 8
bytes of the received block of data as status information (this also includes
error messages).
With the data transmission services SDA, SDN and SRD, the CP
5430 TF/CP 5431 FMS uses the control information from the header of the
block of data to "pack" the data in a frame which can then be transmitted
via the SINEC L2 bus. The remaining 242 bytes are available for the user
data when transmitting and receiving.
B8976060/02 Fundamentals of the Model
3 - 13 Volume 1