Siemens simatic et 200s Operating Instructions Manual page 69

Effect of the Hardware Limit Switches
The two digital inputs (DI0 and DI1) are evaluated by the 1PosInc/Digital as limit switches:
● DI0 is the minus limit switch and limits the operating range in the minus direction.
● DI1 is the plus limit switch and limits the operating range in the plus direction.
You can assign parameters to the hardware limit switches separately as break contacts or
make contacts.
The hardware limit switches are evaluated with linear axes and rotary axes.
Only the hardware limit switch that lies in the direction in which the drive is being moved is
evaluated.
This enables you to move away from a hardware limit switch without additional error
acknowledgment by moving in the other direction if you reach or overrun a hardware limit
switch.
The current signal level of the digital inputs is displayed in the feedback interface, delayed by
the update rate.
You can see from the following table what effect the hardware limit switches have in the
individual MODEs:
MODE
Search for Reference
Inching
Absolute Positioning
Relative Positioning
Starting on the hardware limit switch
Direction
Starting into the operating range
Starting away from the operating range
ET 200S Positioning
Operating Instructions, 05/2007, A5E00124871-04
Effect of the Hardware Limit Switches
The 1PosInc/Digital executes an automatic reversal of direction on the
hardware limit switch.
The motion of the axis is halted on the hardware limit switch, all 3 digital
outputs are set to 0, and the POS_ERR feedback bit is reported.
Response of the 1PosInc/Digital
The 1PosInc/Digital starts the preset MODE.
The POS_ERR=1 feedback bit is set.
1PosInc/Digital
3.6 Functions of the 1PosInc/Digital
69