Siemens S5-135U/155U System Manual page 325

Changeover of the
The operation of Channels 1.0 to 1.7 as inputs or outputs merely depends on
I/O byte
the user program. You define the byte as an input with a read access to the
DI/DQ; you define the byte as an output with a write access. The
double-function of the byte also allows the output byte to be read out.
Unused channels should not be wired nor addressed by program. When these
channels are used as inputs, it should be noted that the corresponding bits in
the output register remain at logic 0. This resetting of output registers is
executed automatically after power-up of the PLC or EU.
Note
When at least one of Channels 1.0 to 1.7 is operated as an input, the
connected sensors and the 1L+ terminal must have the same power supply. If
this is not the case, the input voltage acts on the 1L+ terminal. The resultant
supply to the output amplifiers of Channels 0.0 to 1.7 causes currents to be
drawn via the wired input terminal; these currents may assume different
values, depending on the control states of the outputs.
With the DI/DQ 482, you must set slide switch S2 to setting 1 for operation
without the IP 257.
Figure 8-6
System Manual
C79000-G8576-C199-06
Slide Switch S2
Slide Switch S2 on the DI/DQ 482
Digital Input/Output Modules
Local Bus Interface
8-13