Supplementary information
15.12 Link-up and update sequence
CPU 410-5H Process Automation
292
System Manual, 09/2014, A5E31622160-AB
15.12.4
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 123). 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).
CAUTION
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
System Software for S7-300/400, System
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
S7-400F and S7-400FH Automation Systems.
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.