Technical data

3.3 Application Interfaces of Layer 2 Communication
In this model, as already mentioned, there are two basic types of
communication:
Explicit communication using the existing handling blocks:
➣
S5-S5 communication
➣
Free layer 2 communication
➣
FMA services.
Implicit communication using I/O bytes:
➣
Global I/Os (GP)
➣
Cyclic I/Os (ZP) with the CP 5430 TF
➣
Distributed I/Os (DP).
3.3.1 Explicit Communication
3.3.1.1 S5-S5 Communication
With this type of communication, the CP generates frames from the data
records of the SIMATIC S5 PLC which meet the requirements of the
PROFIBUS standard (Part 1). The services of the first layer and the
FDL-SDA (send data with acknowledge) service of the second layer of the
ISO/OSI reference model are used. Communication between SIMATIC S5
PLCs is achieved using HDBs via S5-S5 links. The job numbers 1 to 32 are
available for transmit jobs via layer 2 and 101 to 132 for receive jobs. The
links to be established between the maximum 32 active stations on SINEC
L2 (static SAP relationships), can be configured with the aid of the COM.
The size of the frames is restricted to a maximum of 128 bytes.
With this type of data transmission, you do not need to know about PDU
structure or service IDs, since the CP does the encoding. To control
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