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You can set specific start times for link-up and update operations at SFC 90 "H_CTRL". For
detailed information on this SFC, refer to Manual
and Standard Functions
Note
If the process tolerates cycle time extensions at any time, you do not need to call SFC 90
"H_CTRL".
The CPU does not perform a self-test during link-up and updating. If you use a fail-safe user
program, you should avoid any excessive delay for the update operation. For more details,
refer to Manual
Example of a time-critical process
A slide block with a 50 mm cam moves on an axis at a constant velocity
v = 10 km/h = 2.78 m/s = 2.78 mm/ms. A switch is located on the axis. So the switch is
actuated by the cam for the duration of ∆t = 18 ms.
For the CPU to detect the actuation of the switch, the inhibit time for priority classes > 15
(see below for definition) must be significantly below 18 ms.
With respect to maximum inhibit times for operations of priority class > 15, STEP 7 only
supports settings of 0 ms or between 100 and 60000 ms, so you need to work around this by
taking one of the following measures:
● Shift the start time of link-up and updating to a time at which the process state is non-
● Use a considerably longer cam and/or substantially reduce the approach velocity of the
16.13
The user program
The rules of developing and programming the user program for the standard S7-400 system
also apply to the S7-400H.
In terms of user program execution, the S7-400H behaves in the same manner as a
standard system. The synchronization functions are integrated in the operating system and
are executed automatically in the background. You do not need to consider these functions
in your user program.
In redundant operation, the user programs are stored identically on both CPUs and are
executed in event-synchronous mode.
However, we offer you several specific blocks for optimizing your user program, e.g., in order
to improve its response to the extension of cycle times due to updates.
Specific blocks for S7–400H
In addition to the blocks that can be used both in S7-400 and in S7-400H, there are
additional blocks for S7-400H. You can use these blocks to influence redundancy functions.
CPU 410-5H Process Automation/CPU 410 SMART
System Manual, 10/2013, A5E32631667-AA
.
S7-400F and S7-400FH Automation Systems
critical . Use SFC 90 "H_CTRL" to set this time (see above).
slide block to the switch.
Supplementary information
16.13 The user program
System Software for S7-300/400, System
.
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