Block Link-Up And Update - Siemens SIMATIC S7-400H Manual

Note
When switching to a CPU with a modified configuration the load memories of the
master and standby may be of different sizes.
5.2.4

Block Link-up and Update

Link-up and update is associated with a scan-cycle time extension. Within this
there is a margin of time in which no I/O updating is performed (see section 5.3
"Time Monitoring"). This must be particularly observed if using remote I/O and a
master/standby switch-over takes place after the update (i.e. in the event of a
configuration modification whilst in operation).
Caution
!
Only perform link-up and update in non-critical process states.
To specify the start time of the link-up and update yourself, the function SFC 90
"H_CTRL" is available. You will find a detailed description of this SFC in the
manual on System Software for S7-300/400, System and Standard Functions ).
Note
If the process tolerates a longer scan-cycle time extension at any point of time,
there is no need to call the 90 "H_CTRL" SFC.
The CPU self-test is not performed during link-up and updating. In the case of a
fail-safe system, therefore, make sure that you do not delay the update over too
long a period. For more details refer to the manual S-7-400F and S7-400FH
Programmable Controllers; Fail-Safe Systems .
Example of a time-critical process
A slide block with a 50 mm long cam moves on an axis at a constant velocity
v = 10 km/h = 2.78 m/s = 2.78 mm/ms. On the axis is a push button. The push
button is thus activated by the cam during a time margin of ∆t = 18 ms.
S7-400H Programmable Controller Fault-Tolerant Systems
A5E00068197-04
Link-up and Update
5-13