Reducing The Reaction Time - Siemens SIMATIC S7-400 Reference Manual

I/O Direct Accesses
You can achieve faster reaction times by direct access to the I/O in the user
program, for example with
• L
PIB
• T
PQW
you can avoid the reaction times in part, as described above.

Reducing the Reaction Time

In this way the maximum reaction time is reduced to
• 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 3-8
Type of Access
Read byte
Read word
Read double word
Write byte
Write word
Write double word
Read byte in the
expansion rack with
local link
Read byte in the
expansion rack with
remote link
The specified times are merely CPU processing times and apply, unless otherwise
stated, to signal modules in the central rack.
Note
You can similarly achieve fast reaction times by using hardware interrupts; refer to
Section 3.8.
Automation System S7-400 CPU Specifications
A5E00165965-01
or
Reducing the Reaction Time
CPU CPU
412-1 414-2
412-2 414-3
2.6 ms 2.1 ms
4.1 ms 3.5 ms
8.0 ms 7.0 ms
2.7 ms 2.2 ms
4.2 ms 3.7 ms
8.3 ms 7.4 ms
11.6 ms 10.6 ms
17.2 ms 16.2 ms
Cycle and Reaction Times of the S7-400
CPU CPU CPU 41x-4H
416-2 417-4 single
416-3 mode
m
2.0 ms
2.4 s 34
m
3.4 ms
3.8 s 37
m
6.7 ms
7.6 s 41
m
2.1 ms
2.4 s 29
m
3.6 ms
3.9 s 32
m
7.1 ms
7.8 s 36
5.3 ms 10.6 ms
–
10.1 ms 16.2 ms
–
CPU
41x-4H
redundant
m m
s 64 s
m m
s 67 s
m m
s 71 s
m m
s 58 s
m m
s 61 s
m m
s 65 s
–
–
3-17