Disabling Of Link-Up And Update - Siemens SIMATIC CPU 410 System Manual

Supplementary information
18.13 Link-up and update sequence
18.13.4

Disabling of link-up and update

Link-up and update entails a cycle time extension. This includes a period during which no I/O
updates are performed; see Chapter Time monitoring (Page 120). You must pay special
attention to this if you are using distributed I/O and a master/standby changeover occurs
after the update (thus, when the configuration is modified during operation).
Always perform link-up and update operations when the process is not in a critical state.
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-
critical . Use SFC 90 "H_CTRL" to set this time (see above).
● Use a considerably longer cam and/or substantially reduce the approach velocity of the
slide block to the switch.
352
CAUTION
.
S7-400F and S7-400FH Automation Systems
System Software for S7-300/400, System
.
CPU 410 Process Automation/CPU 410 SMART
System Manual, 05/2017, A5E31622160-AC