Pcp Communication - Bosch Rexroth ID 40 Manual

68/176 Interbus
Bosch Rexroth AG, MIT: ID 40, 3 842 530 344/2014-05
PROOF COPy 1 | 20.05.2014 | FOR INTERNAL USE ONLy
8.3.1

PCP communication

Before data can be exchanged between two PCP Interbus users, a logical
connection has to exist between them. These logical connections are referred
to as communication relationships. Specific connection parameters for such a
communication relationship are stored in what is known as the communication
relationships list (CRL).
Each communication relationship contains a communication reference number
(CR). This uniquely identifies the communication relationship. With the CR, the PCP
function block of a PLC with an Interbus master module can access the individual
devices via PCP communication.
Both the CRL and the CR are Interbus standard and are established when Interbus is
started up (see Chapter 11.2 "Starting up Interbus").
One CRL parameter - the maximum possible PDU length - can be modified on the
SLK (see Chapter 11.2.2 "Configuring the maximum PDU size for the PCP channel").
The PDU (Protocol Data Unit) determines the maximum size of the SLK's transmit
and receive buffer and with it the data packet that can be transmitted via PCP
communication. This makes it possible to adjust the amount of MDT data (payload
amount) transmitted in the application.
Table 20: Payload amount in every subindex 3 of every 5FF object depending on PDU size (npdu):
Object Interbus data type
5FF4
0x0042
5FF5 0x0041
5FF6
Payload amount in subindex 3 [bytes]
npdu - 7
npdu - 9