Consistent Reading And Writing Of Data From And To Dp Standard Slaves/Io Devices - Siemens CPU 410-5H Process Automation System Manual

Supplementary information
16.11 Consistent data
16.11.3 Consistent reading and writing of data from and to DP standard slaves/IO
devices
Reading data consistently from a DP standard slave using SFC 14 "DPRD_DAT"
Using SFC 14 "DPRD_DAT" (read consistent data of a DP standard slave), you can
consistently read the data of a DP standard slave of IO device.
if no error occurred during the data transmission, the data read is entered into the destination
area defined by RECORD.
The destination area must have the same length as the one you have configured for the
selected module with STEP 7.
By calling SFC 14 you can only access the data of one module/DP identifier at the
configured start address.
For information on SFC 14, refer to the corresponding online help and to Manual "System
and Standard Functions".
Note
Evaluate the entire currently used part of the receive area RD_i before you activate a new
job.
Writing data consistently to a DP standard slave using SFC 15 "DPWR_DAT"
Using SFC 15 "DPWR_DAT" (write consistent data to a DP standard slave), you transmit the
data in RECORD consistently to the addressed DP standard slave or IO device.
The source area must have the same length as the one you configured for the selected
module with STEP 7.
For information on SFC 15, refer to the corresponding online help and Manual "System and
Standard Functions".
Note
When a send operation is activated (positive edge at REQ), the data to be transmitted from
the send areas SD_i is copied from the user program. You can write new data to these areas
after the block call command without corrupting the current send data.
Upper limits for the transfer of consistent user data to a DP slave
The PROFIBUS DP standard defines upper limits for the transfer of consistent user data to a
DP slave. For this reason a maximum of 64 words = 128 bytes of user data can be
consistently transferred in a block to the DP standard slave.
You can define the length of the consistent area in your configuration. In the special
identification format (SIF), you can define a maximum length of consistent data of 64 words =
128 bytes: 128 bytes for inputs and 128 bytes for outputs. A greater length is not possible.
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CPU 410-5H Process Automation/CPU 410 SMART
System Manual, 10/2013, A5E32631667-AA