Table 16-9 Direct Access Of The Cpus To I/O Modules - Siemens SIMATIC S7-400H System Manual

I/O direct access
You can achieve faster reaction times with direct access to the I/O in your user program, for
example with
● L PIB or
● T PQW.
You can work around the reaction times as shown earlier.
Reducing the reaction time
This reduces the maximum reaction time to
● Delay at 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
times shown are "ideal values".
Table 16-9 Direct access of the CPUs to I/O modules
Access mode 412-3H
stand-alone
mode
Read byte 3.5 µs
Read word 5.2 µs
Read double word 8.2 µs
Write byte 3.5 µs
Write word 5.2 µs
Write double word 8.5 µs
Table 16-10 Direct access of the CPUs to I/O modules in the expansion unit with local link
Access mode 412-3H
stand-alone
mode
Read byte 6.9 µs
Read word 12.1 µs
Read double word 22.2 µs
Write byte 6.6 µs
Write word 11.7 µs
Write double word 21.5 µs
S7-400H
System Manual, 09/2007, A5E00267695-03
412-3H 414-4H
redundant stand-alone
mode
30.5 µs 3.0 µs
33.0 µs 4.5 µs
33.0 µs 7.6 µs
31.1 µs 2.8 µs
33.5 µs 4.5 µs
33.5 µs 7.8 µs
412-3H 414-4H
redundant stand-alone
mode
32.6 µs 6.3 µs
36.5 µs 11.5 µs
46.5 µs 21.5 µs
31.6 µs 5.9 µs
36.7 µs 11.0 µs
46.4 µs 20.8 µs
S7-400 cycle and reaction times
414-4H 417-4H
redundant stand-alone
mode
21.0 µs 2.2 µs
22.0 µs 3.9 µs
23.5 µs 7.0 µs
21.5 µs 2.3 µs
22.5 µs 3.9 µs
24.0 µs 7.1 µs
414-4H 417-4H
redundant stand-alone
mode
22.5 µs 5.7 µs
27.5 µs 10.8 µs
37.5 µs 20.9 µs
22.5 µs 5.5 µs
27.5 µs 10.4 µs
37.0 µs 20.2 µs
16.5 Reaction time
417-4H
redundant
11.2 µs
11.7 µs
14.7 µs
11.3 µs
11.8 µs
15.0 µs
417-4H
redundant
13.4 µs
18.6 µs
28.7 µs
13.4 µs
18.3 µs
28.0 µs
275