Siemens SIMATIC S7-400H System Manual page 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
Read byte 3.0 µs
Read word 4.0 µs
Read double 7.0 µs
word
Write byte 3.0 µs
Write word 4.0 µs
Write double 7.5 µs
word
S7-400H
System Manual, 03/2012, A5E00267695-11
412-5H 414-5H
redundant stand-
alone
mode
33.9 µs 2.6 µs
33.9 µs 4.0 µs
33.9 µs 7.0 µs
33.9 µs 2.6 µs
33.9 µs 4.0 µs
7.4 µs
33.9 µs
414-5H 416-5H
redundant stand-
alone
mode
21.0 µs 2.3 µs
24.5 µs 4.0 µs
24.5 µs 7.0 µs
21.5 µs 2.4 µs
24.5 µs 4.0 µs
24.5 µs 7.3 µs
S7-400 cycle and response times
19.5 Response time
416-5H 417-5H
redundant stand-
alone
mode
15.9 µs 2.2 µs
16.2 µs 3.9 µs
17.2 µs 7.0 µs
16.0 µs 2.3 µs
16.2 µs 3.9 µs
18.5 µs 7.1 µs
417-5H
redundant
11.2 µs
11.7 µs
14.7 µs
11.3 µs
11.8 µs
15.0 µs
373