Siemens SINUMERIK 840D sl TCU 30.3 Manual page 43

Operating principle
If the TCU_SHIFT_LOCK bit is set for switchover disable, a user authorization request is not
carried out independently of the mode set on the HMI for allocation of user authorizations (veto
mode), i.e., a change of user authorization is rejected.
This message appears on all OPs for approximately 5 seconds:
"No switchover: Switchover disable set in current PLC."
While this message is displayed, operations on the OP with the user authorization can still be
carried out unaffected.
Note
The switchover disable only relates to changing the user authorization on the OPs in a
shadowing grouping on a PCU.
Active switching from one OP to another PCU is not prevented.
Special features
The following special cases should be noted:
● Even if switchover disable is set, the TCU_INDEX field value may change in the PLC. This
is the case if:
– The OP in possession of the user authorization is actively switched to another PCU.
– An m:n switchover is in progress. The HMI program of the incoming PCU deactivates
– A PCU is disconnected from a NCK/PLC in the context of m:n. No HMI program and,
● If a TCU is actively switched over to another PCU, it can be deactivated there, i.e. it does
not obtain the user authorization, if a switchover disable is set for the destination PCU.
● With an m:n PCU switchover – the PCU is switched to another NCK and, therefore, to
another PLC – the PCU takes on the switchover disable settings of that PLC.
● The m:n interlock options on the PLC side have priority over the TCU switchover disable,
so that a set TCU switchover disable cannot prevent an m:n switchover. If necessary, the
m:n interference options should be synchronized here with those for the TCU in the PLC.
It may, for example, be practical to set or remove the m:n displacement disable
simultaneously with the TCU switchover disable.
TCU 30.3
Manual, 09/2017, A5E40874197
Depending on whether another TCU takes on the user authorization or whether no TCU
is currently active, either the index of the TCU or the PCU itself (if its directly connected
OP becomes active) is entered, in exactly the same way as when there is a user
authorization switchover.
This can also be the value 255, if no TCU index is available for the OP. 0 is entered if
an OP is no longer available in the shadow grouping.
the HMI program which is active on it. An OP from the shadow grouping of the new
(incoming) PCU must receive the user authorization. The TCU index of this OP is
entered in the TCU_INDEX field.
therefore, no OP with user authorization is then available on the exited NCK/PLC. This
is signaled independently of a switchover disable by entering the value 0 into the
TCU_INDEX field.
Networking
5.2 Commissioning TCU
43