Siemens SIMATIC S7-400 Reference Manual page 50

Structure of a CPU 41x
Further Information
You can find descriptions and information on changing from PROFIBUS DP to
PROFIBUS DPV1 on the Internet at the following address:
http://www.siemens.com/automation/service&support
Under the item number 7027576
Monitor/Modify, Programming via PROFIBUS
As an alternative to the MPI interface, you can use the PROFIBUS DP interface to
program the CPU or execute the programming device functions Monitor and
Modify.
Note
The applications Programming and Monitor/Modify via the PROFIBUS DP
interface extend the DP cycle.
Equidistance
Equidistance is the property of the PROFIBUS DP that guarantees bus cycles of
exactly identical length. "Identical length bus cycles" means that the DP master
always begins the DP bus cycle after the same time interval. From the view of the
slaves, this means that they receive their data from the master at the exact same
time intervals.
As of STEP7 V 5.2, you can configure equidistant bus cycles for PROFIBUS
subnetworks.
Consistent data
Data that belongs together in terms of its content and a process state written at a
specific point in time is known as consistent data.. To maintain consistency, the
data should not be changed or updated during processing or transmission.
A detailed description is available in Chapter 1.13.
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Automation System S7-400 CPU Specifications
A5E00165965-01