Configuring Hardware and Communication Connections STEP 7.pdf

Configuring the Distributed I/O (DP)
3.3 Distributed Reading and Writing of Consistent Data
(> 4 Bytes)
Previously, you were able to access consistent data (> 4 Bytes) on a DP slave by
means of SFC 14 and SFC 15.
As of Version 3.0 of CPU 318-2 and CPUs 41x, you can also access a consistent
data area by accessing the process image (such as L IW).
Configuring Consistent Data Areas > 4 Bytes
1. In the hardware configuration, select the "Addresses" tab for the DP slave.
Depending on the type of DP slave, the consistency area either has standard
default settings and cannot be changed (such as specified by a GSD file), or
you can define the consistency area in the fields "Length", "Unit" and
"Consistency via".
2. If necessary, define the length of the consistent area and enter this area into a
process image. To do this proceed as follows: In the "Process image partition"
field, select OB1-PI or, in the case of S7-400, select yet another process-image
partition (PIP) such as PIP 3. If you do not put the data in a process image
partition, then you must use SFC 14 or SFC 15 for data exchanges.
Upon update of the process image, the operating system transfers these data
consistently, and you can use download and transfer commands to access the data
in the process image. This provides you with an easy and efficient (low run-time
load) way to access consistent data.
Configuring Hardware and Communication Connections with STEP 7
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