Siemens SIMATIC S7-1500 Function Manual page 19

Time sequence of synchronization
4.1 Time sequence of synchronization on PROFINET IO and PROFIBUS DP
From reading-in of input data to outputting of output data
The basic time sequence of all components involved in synchronization is explained in the
following:
①
Measured value acquisition in the process
②
Isochronous read-in of input data
③
Transport of input data to the IO controller/DP master (CPU) via the subnet
④
Further processing in the isochronous application of the CPU
⑤
Transport of output data to the outputting IO device/DP slave via the subnet
⑥
Isochronous output of output data
T_DC Data cycle (Time_DataCycle)
T Time for reading in the input data
I
T Time for outputting the output data
O
T Configured delay time
V
Figure 4-1 Time sequence of synchronization on PROFINET IO/PROFIBUS DP
So that all input data is ready for transport via the subnet at the next start of the
PROFINET IO-/PROFIBUS DP cycle, the start of the I/O read-in cycle is advanced by the
amount of lead time T
at this time. T
backplane bus times and the like. The lead time T
Let the lead time T
ensures that a common, minimum T
18
. T is the "flashbulb" for the inputs. All synchronized inputs are read in
I I
is necessary in order to compensate for analog-to-digital conversion,
I
be assigned automatically by STEP 7. With the default setting, STEP 7
I
I
can be configured by STEP 7 or by you.
I
is set.
Function Manual, 10/2018, A5E43884988-AA
Isochronous mode