Siemens SIMATIC PCS 7 System Manual page 299

Processing direct I/O access
You can achieve faster response times by directly accessing the I/O in your user program,
e.g., with the following instructions:
● L PIB
● 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
● Runtime of the user program (can be interrupted by higher-priority interrupt processing)
● Runtime of direct access
● 2x bus runtime 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 16- 15 Direct access of the CPUs to I/O modules in the central controller
Access type
Read byte
Read word
Read double word
Write byte
Write word
Write double word
Table 16- 16 Direct access of the CPUs to I/O modules in the expansion unit with local link
Access type
Read byte
Read word
Read double word
Write byte
Write word
Write double word
CPU 410-5H Process Automation/CPU 410 SMART
System Manual, 09/2014, A5E32631667-AB
16.15 Cycle and response times of the CPU 410-5H
CPU 410-5H
stand-alone mode
2.2 µs
3.7 µs
6.8 µs
2.2 µs
3.8 µs
7.0 µs
CPU 410-5H
stand-alone mode
5.5 µs
10.5 µs
19.9 µs
5.3 µs
10.2 µs
19.8 µs
Supplementary information
CPU 410-5H
redundant
11.0 µs
11.1 µs
14.2 µs
10.8 µs
11.2 µs
14.4 µs
CPU 410-5H
redundant
13.0 µs
17.9 µs
27.4 µs
12.7 µs
17.6 µs
27.3 µs
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