Siemens Simatic S7-400 - Page 142

Cycle and Response Times of the S7-400
9.5 Reaction Time
S7-400 Automation System, CPU Specifications
9-16 Manual, 10/2006, 6ES7498-8AA04-8BA0
I/O Direct Accesses
You can reach faster response times with direct access to the I/O in your user program. For
example, you can partially circumvent the response times as described above by using one
of the following commands:
● L PIB
● T PQW
Reducing the Response Time
In this way the maximum response time is reduced to the following components:
● Delay in the inputs and outputs
● Runtime of the user program (can be interrupted by high-priority interrupt handling)
● Runtime of direct accesses
● Twice the bus transit time of DP
The following table lists the execution times of direct accesses by the CPU to I/O modules.
The times shown are "ideal values".
Table 9-6 Reducing the Response Time
Access mode CPU 414 CPU 416
I/O module
Read byte
Read word
Read double word
Write byte
Write word
Write double word
2.6 µs
4.2 µs
7.2 µs
2.3 µs
3.6 µs
6.2 µs
2.5 µs
4.0 µs
7.1 µs
2.2 µs
3.4 µs
5.9 µs
Expansion rack with local connection
Read byte
Read word
Read double word
Write byte
Write word
Write double word
6,0 µs
11,0 µs
21,0 µs
5,4 µs
10,1 µs
19,5 µs
5,7 µs
10,8 µs
20,8 µs
5,4 µs
10,0 µs
19,4 µs
Read byte in the expansion rack with remote connection
Read byte
Read word
Read double word
Write byte
Write word
Write double word
11,3 µs
22,8 µs
45,9 µs
10,8 µs
21,9 µs
44,0 µs
11,3 µs
22,8 µs
45,9 µs
10,8 µs
21,9 µs
44,0 µs
The specified times are merely CPU processing times and apply, unless otherwise stated, to
signal modules in the central rack.