Reading Data Consistently From A Dp Standard Slave And Writing Consistently To A Dp Standard Slave - Siemens SIMATIC S7-400H System Manual

7.2.4 Reading data consistently from a DP standard slave and writing consistently to a
DP standard slave
Reading data consistently from a DP standard slave using SFC 14 "DPRD_DAT"
Use SFC 14 "DPRD_DAT", "read consistent data of a DP standard slave", to read consistent
data from a DP standard slave.
The data read is entered into the destination range defined by RECORD if no error occurs
during the data transmission.
The destination range 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 ID at the configured
start address.
Writing data consistently to a DP standard slave using SFC 15 "DPWR_DAT"
Use SFC 15 "DPWR_DAT", "write consistent data to a DP standard slave", to transfer
consistent data in RECORD to the addressed DP standard slave.
The source area must be the same length as the one you have configured for the selected
module with STEP 7.
Upper limit 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 slave.
You can define the length of 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. Any greater length value is not possible.
This upper limit applies only to pure user data. Diagnostics and parameter data will be
grouped to form complete data records, and are thus always transferred consistently.
In the general identification format (GIF), you can define a maximum length of consistent
data of 16 words = 32 bytes, 32 bytes for inputs, and 32 bytes for outputs. Any greater length
value is not possible.
In this context, make allowances for the fact that a 41x CPU operating as DP slave generally
has to support its configuration at an external master (implementation by means of GSD file)
using the general identification format. A 41x CPU operated as DP slave thus supports only
a maximum length of 16 words = 32 bytes in its transfer memory for PROFIBUS DP.
S7-400H
System Manual, 09/2007, A5E00267695-03
S7-400H in PROFIBUS DP mode
7.2 Consistent Data
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