Technical data

5.5 Data Transmission with Distributed I/Os (DP)
Data transmission via L2-DP (distributed I/Os) provides a standardized
interface for communication between SIMATIC S5 PLCs and field devices
(DP slaves).
Data transmission with DP is simple to handle.
For the user, the programming and handling is reduced to a minimum.
When using the DP service, part of the I/O area of the PLC is occupied by
the connected DP slaves with the CP modeling the I/O bytes towards the
CPU. This means that access by the user program to the I/O bytes used for
L2-DP is acknowledged by the CP.
Using the L2-DP protocol, the inputs and outputs assigned to the individual
DP slaves are exchanged cyclically by the CP (see Chapter 11).
This type of communication has the following characteristics:
➣ Data transmission uses one of the following two methods:
– Synchronized with the cycle, determined by the STEP 5 control
program.
– Free, initiated by the CP (no influence by the STEP 5 control
program).
➣ The CP can only be operated as DP master of class 1 on the SINEC L2
bus.
➣ The L2-DP interface of the CP operates according to the PROFIBUS
standard DIN E 19254, Part 3.
Special features:
With this type of communication, the base interface is always used.
Selecting the Type of Communication B8976060/02
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