Siemens S5-135U/155U System Manual page 327

Figure 8-7
The address byte under which the module is referenced by the STEP 5
program is independent of the slot.
Start Address For modules with 16 or 32 inputs or outputs, i.e. 2 or 4 bytes, only the lowest
address (start address) is set for the first byte. The addresses of the following
bytes of the same module are decoded on the module.
If, for example, the address 20 is set for a 16-bit module (2 bytes), the
following address 21 is decoded internally and is no longer available. The
next free address would be 22.
For a 32-bit module (4 bytes) with start address 20, addresses 21, 22 and 23
would be decoded internally. The next free address would be 24.
Addresses already assigned must not be set again.
However, digital input and output modules may be given the same address
because they are referenced by different commands in the user program.
System Manual
C79000-G8576-C199-06
On Setting
(Switch Pressed)
Address (Decimal)
Labeling of the Addressing Switch (Extract from Module Labeling)
Digital Input/Output Modules
Addressing Switch
Labeling Field for the
Module Address and
Marked Switch Settings
Binary Significance
of the Address Bit
Address Bit
8-15