PROFIBUS Communication
3/19
WL Circuit Breaker
Example: Reading and Writing
Data Records with an S7
This example is based on an S7-300
CPU with an integrated DP interface
and STEP7 Version 5.1.
Writing data records
In this example, SFC58 is used to
write the protection parameters to
DS129. The data is stored in DB 129
and contains the current parameters,
which are to be sent to the circuit
breaker. In this example, the logical
base address is the same for the
inputs and outputs, this is, ID
‘W#16#54’ is specified. The request
is triggered with an edge on marker
M20.0 and reset with an edge on
M20.1 once it has been processed
successfully, enabling the user
to control how the data record is
written. The time required to process
the request depends on the system
configuration and may take several
CPU cycles.
If a fault occurs, MW22 is available
for information purposes. For more
information, refer to the reference
manual “System Manual for S7
300/400 System and Standard
Functions.”
Recording data records
In this example, DR94 (operating
data) is read using SFC59. The data
is stored in DB 94 and contains the
current circuit breaker operating
data.
Since the operating principle and
parameters are identical to system
function SFC58, it will not be
discussed in any further detail here.
Figure 3-10
The STEP7 program code shows how the entire DR129 is written from DB129 to
the device. The write process is triggered once by marker M20.0
Figure 3-11
This program example shows how DR94 is read and stored in DB94 in STEP7.
The process is triggered by setting marker M20.4. Cyclic updates are not carried out.
WL PROFIBUS Communication and Electronic Accessories • July 2004
