Siemens SIMATIC S5 Manual page 97

Principle of Operation
- Stop command
- Automatically
I
owing to error
- Operator error
Fig, 4/3 Relationship between operating instruction and axis status
You can only change or start a mode in the axis status "finished", This is achieved by the start,
forward or reverse command in conjunction with the required mode.
Operating instructions entered while a mode is running result in the error message "job not per-
mitted" and the current action is terminated. If an operating instruction is simply incorrect, the
axis remains in the "finished" status.
The axis can change from the "running" status to the "finished" status for a number of reasons.
These include the following:
a stop command in a mode,
a start command in the "axis off" mode,
an operator error (e.g. "enter" command with a different mode),
an error resulting from an external event (e.g. external stop command or a limit switch
being tripped) or
the correct completion of a job (e.g. approach to a particular target point or entry of ma-
chine data).
The enter command is required for the following tasks:
to trigger a single traversing movement in the "automatic single statement" mode,
to acknowledge a "programmed ha!t" in the "automatic" or "automatic single statement"
modes,
to continue an interrupted machining program,
to store statements in the teach-in mode.
4 - 4
"Enter" command (continuation)
Operator error
1
start
forward
reverse