Siemens Sinumerik 840D sl Programming Manual page 645

Interlocking synchronized actions
Modal synchronized actions with ID numbers <n> = 1 ... 64 can be interlocked from the PLC.
The associated condition is no longer evaluated and execution of the associated function is
locked in the NCK.
All synchronized actions can be locked indiscriminately with one signal in the PLC interface.
Note
A programmed synchronized action is active as standard and can be protected against
overwriting/locking by a machine data setting.
It should not be possible for end users to modify synchronized actions defined by the
machine manufacturer.
Examples
Example 1: Lock synchronized actions (LOCK)
Program code
N100 ID=1 WHENEVER $A_IN[1]==1 DO M130
...
N200 ID=2 WHENEVER $A_IN[2]==1 DO LOCK(1)
Example 2: Unlock synchronized actions (UNLOCK)
Program code
N100 ID=1 WHENEVER $A_IN[1]==1 DO M130
...
N200 ID=2 WHENEVER $A_IN[2]==1 DO LOCK(1)
...
N250 ID=3 WHENEVER $A_IN[3]==1 DO UNLOCK(1)
Example 3: Interrupt technology cycle (RESET)
Program code
N100 ID=1 WHENEVER $A_IN[1]==1 DO M130
...
N200 ID=2 WHENEVER $A_IN[2]==1 DO RESET(1)
Job planning
Programming Manual, 02/2011, 6FC5398-2BP40-1BA0
Motion synchronous actions
10.5 Technology cycles
645