S7-400 cycle and response times
19.5 Response time
S7-400H
System Manual, 03/2012, A5E00267695-11
373
Processing direct I/O access
You can achieve faster response times with direct access to the I/Os in your user program,
e.g. with the following operations:
●
L PEB
●
T PQW
However, note that any I/O access requires a synchronization of the two units and thus
extends the cycle time.
Reducing the response time
This reduces the maximum response time to
●
Delay of the inputs and outputs
●
User program execution time (can be interrupted by higher-priority interrupt handling)
●
Runtime of direct access
●
Twice the bus delay time of DP
The following table lists the execution times of direct access by the CPU to I/O modules. The
specified times are pure CPU processing times and do not include the processing times of
the signal modules.
Table 19- 10 Direct access of the CPUs to I/O modules in the central rack
Access mode
412-5H
stand-
alone
mode
412-5H
redundant
414-5H
stand-
alone
mode
414-5H
redundant
416-5H
stand-
alone
mode
416-5H
redundant
417-5H
stand-
alone
mode
417-5H
redundant
Read byte
Read word
Read double
word
Write byte
Write word
Write double
word
3.0 µs
4.0 µs
7.0 µs
3.0 µs
4.0 µs
7.5 µs
33.9 µs
33.9 µs
33.9 µs
33.9 µs
33.9 µs
33.9 µs
2.6 µs
4.0 µs
7.0 µs
2.6 µs
4.0 µs
7.4 µs
21.0 µs
24.5 µs
24.5 µs
21.5 µs
24.5 µs
24.5 µs
2.3 µs
4.0 µs
7.0 µs
2.4 µs
4.0 µs
7.3 µs
15.9 µs
16.2 µs
17.2 µs
16.0 µs
16.2 µs
18.5 µs
2.2 µs
3.9 µs
7.0 µs
2.3 µs
3.9 µs
7.1 µs
11.2 µs
11.7 µs
14.7 µs
11.3 µs
11.8 µs
15.0 µs