Siemens SINUMERIK 840D sl Manual page 45

HMI ↔ PLC data interface
The "switchover disable" function is always active and does not have to be switched on
explicitly. The function is controlled by a data bit in the PLC. The HMI transfers the active OP
to the PLC, thus forming the basis of the control function in the PLC.
The control bits and control information for this function are stored in the m:n data interface of
the PLC. In terms of m:n, this function can be operated separately for the currently overridden
HMIs in both m:n online interfaces (DB19.DBW120 ff for HMI1 and DB19.DBW130 ff for HMI2).
If a system is not running an m:n, only the first m:n online interface is used for this function.
Switchover disable is controlled by a TCU_SHIFT_LOCK bit, managed by the user, on each
HMI in the PLC. The bit address for the first HMI is DB19.DBB126.6 and DB19.DBB136.6 for
the second HMI.
The PLC m:n online interface is expanded so that byte DB19.DBB118 is also assigned to the
first interface and byte DB19.DBB119 to the second. These bytes acquire the index of the
active TCU/OP for the appropriate HMI. The byte is called TCU_INDEX. The appropriate HMI
uses the TCU index configured for the active TCU to describe the TCU_INDEX byte.
The TCU_SHIFT_LOCK bit is monitored by the appropriate HMI. A value = 1 triggers the
switchover disable. Switchover is enabled if the value returns to 0. The TCU_SHIFT_LOCK bit
can be set, for example, to the PLC by the user pressing a key or it can be managed by the PLC
user program according to its own logic. The TCU_SHIFT_LOCK bit is managed in the PLC
exclusively by the user; the HMI only accesses this bit in read-only mode.
The HMI assigns the TCU_INDEX field with the configured index to the TCU or PCU/IPC with
an OP that currently possesses user authorization in the shadow group. If no OP is active, a
value of 0 is entered in TCU_INDEX.
If no TCU index is configured for the active TCU/OP, the value 255 = undefined is transferred
as a TCU index. This means that the values 0 and 255 may not be configured as the TCU index.
Configuration
The TCU index is configured on the PCU/IPC in the same way as a machine control panel
address (MCP address). The TCU index is set in the "OP Properties" dialog of the "System
Network Center" program.
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."
Operator panel front: OP 012
Manual, 05/2019, A5E36371591B AB
Networking
5.2 Commissioning TCU
45