Technical data

Table Of Contents
SFCs for Distributed I/Os or PROFINET IO
System Software for S7-300/400 System and Standard Functions - Volume 1/2
A5E00709327-01
16-19
16.5 Reading Consistent Data of a DP Standard
Slave//PROFINET IO Device with SFC 14 "DPRD_DAT"
Data Consistency
Refer to the section Overview of S7 Communication and S7 Basic Communication
- Data Consistency.
Purpose of SFC 14
You require SFC 14 "DPRD_DAT" because you can only read out a maximum of
four continuous bytes using load instructions that access the I/Os or the process
image input table.
Note
If required, you can also read consistent data via the process image of the inputs.
To determine whether the CPU supports this functionality, refer to the "S7-300
Programmable Controller, Hardware and Installation" manual.
All S7-400 CPUs support this functionality.
!
Caution
When using SFC 14 "DPRD_DAT", avoid accessing I/O areas that have process
image partitions with OB6x connections (clocked interrupts) assigned to them.
Description
With SFC 14 "DPRD_DAT" (read consistent data of a DP standard slave), you read
the consistent data of a DP standard slave/PROFINET IO device.
To find the maximum length that applies here, refer to the following manuals:
S7-300 Programmable Controller, Hardware and Installation
ET 200S Interface Submodule, IM151-7 CPU
Base Submodule BM147CPU
For S7-400 CPUs the maximum length is 32 bytes.
If no error occurred during the data transfer, the data that have been read are
entered in the destination area identified by RECORD.
The destination area must have the same length as configured for the selected
module with STEP 7.