Siemens Simatic S7-1500 Function Manual page 44

Factors
To determine the process response time, you must take account of the following factors in
addition to the CPU response time described above:
● Delay of the inputs and outputs at the I/O module
● Switching times of the sensors and actuators used
● Update times for PROFINET IO or DP cycle times on PROFIBUS DP; update time of the
backplane bus for ET 200SP CPUs
Delay at the inputs and outputs of the modules
The delay and cycle times can be found in the technical specifications of the I/O modules.
Update times for PROFINET IO and DP cycle times on PROFIBUS DP
When distributed I/O is used, the maximum response time is additionally extended by the
bus transmission times of PROFIBUS or PROFINET. These bus transmission times occur
during both the reading and output of the process image partitions. The bus transmission
times correspond to the bus update cycle of the distributed device.
PROFINET IO
If you use STEP 7 to configure your PROFINET IO system, STEP 7 calculates the update
time. To display the update time, follow these steps:
● Select the PROFINET interface of the I/O module.
● In the General tab, select "Advanced options > Real time settings > IO cycle".
The update time is displayed in the "Update time" field and can be set for each IO device.
PROFIBUS DP
If you use STEP 7 to configure your PROFIBUS DP master system, STEP 7 calculates the
DP cycle time. To display the DP cycle time, follow these steps:
● Select the PROFIBUS subnet in the network view.
● In the General tab of the Inspector window, navigate to the Bus parameters.
The DP cycle time is displayed in the "Parameters" field at "Typical Ttr".
The following figure illustrates the additional bus runtimes using distributed I/O.
Figure 3-11
A further optimization of the response times is achieved by using isochronous mode.
Cycle and response times
Function Manual, 10/2018, A5E03461504-AD
3.4 Response time for cyclic and time-driven program execution
Additional bus runtimes with distributed I/O
Cyclic program execution
43