Technical data

7.1 Basics of Data Transmission with HDBs on
Configured S5-S5 Links
The following applies for the CP 5430 TF/CP 5431 FMS:
The firmware of the module generates frames from the data records of the
SIMATIC S5 PLC which meet the requirements of the PROFIBUS standard.
The services of the first and second layers of the ISO/OSI reference model
are used.
You should understand the following points:
➣ What is meant by S5-S5 links and what are the characteristics of such
links?
➣ How is data transmission via such links controlled?
Characteristics of the S5S5 link
➣ S5-S5 links allow reliable data exchange between two SIMATIC PLCs
using the SEND and RECEIVE handling blocks.
➣ The start and end points of an S5-S5 link are service access points
(SAPs).
➣ An SAP manages the link and provides the application process with
services for data transmission.
➣ 64 SAPs are defined, of which the SAPs 2 to 54 are available for this
type of transmission.
➣ The links between the PLCs created with COM 5430 TF/COM 5431
FMS use SAPs 2 to 54. Each SAP can be assigned a particular send or
receive job number (refer to Table 7.1). The number of possible SAPs
may be restricted if other types of data transmission are used.
➣ An S5-S5 link must be assigned the priority "Low", "High" or "Interrupt"
(refer to Section 7.2.1).
S5-S5 Communication B8976060/02
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