Configuring Hardware and Communication Connections STEP 7.pdf

13.4 Response Time
Configuring Global Data Communication
The response time for two stations that exchange GD packets via an MPI subnet
can be calculated approximately.
Requirement for Calculating the Response Time
Calculation
Tip
• Transmission rate 187.5 kbit/s
• No other communication by means of MPI (for example, by connected
programming devices or operator panels)
response time ≈ scan rate (sender) × scan cycle time (sender) + scan rate
(receiver) × scan cycle time (receiver) + number (of MPI nodes) × 10 ms
For higher transmission rates, the factor "× 10 ms" is smaller; however, this factor
does not diminish linearly with an increase in transmission speed.
Because the response time is very dependent on the scan cycle times and on the
other communication load over the MPI, you must determine the response time in
your system empirically and, where appropriate, adapt the scan rate.
Configuring Hardware and Communication Connections with STEP 7
A5E00706939-01 13-11