Siemens SIMATIC S5 Manual page 95

Principle of Operation
With certain operating instructions (transferring a machine data to the IP247), data are also sent
to the module along with the instruction. The reactions in this case are explained in the descrip-
tion of the modes.
Monitoring commands are used to fetch the axis attributes (checkback signals), the module er-
rors and information about the actual value and distance to go from the module cyclically. They
are independent of the operating instructions and can be sent to the module at any time. They
are processed immediately. The next monitoring command can only be input to an interface
when the previous command has been processed. Monitoring commands can be sent to the
positioning module simultaneously by both interfaces, without the commands interfering with
each other.
Fig, 4/1 Operating instructions and monitoring commands
Error messages resulting from incorrect operation or an external event (e.g. limit switch re-
sponded) are not reset until they are acknowledged by the input of a new operating instruction at
one of the two interfaces. Between the error message and the acknowledgement, any number of
monitoring commands can be entered: the unacknowledged error will continue to be output
along with the monitoring information.
Each of the axes is always in one of the operating modes. After power on, the "axis off" mode
(see below) is set. Within each mode, an axis can be active or idle. This is expressed by the "axis
status" which can have the values "running" or "finished" (=> Section 2.7 "The Axis Attributes").
The axis status can be interrogated via both interfaces. The axis status appears in the test dis-
play on the PG; on the PC side it can be read in the checkback signals using FBI 64.
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