Siemens S5-155U System Manual page 316

Installation and Startup
Start address
8 - 18
On Setting
(Switch Pressed)
Address (Decimal)
Figure 8-7 Labelling of the Addressing Switch
(Extract from Module Labelling)
The address byte under which the module is referenced by the STEP 5
program is independent of the slot.
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.
Addressing Switch
Labelling field
for the module address
and marked switch
settings
Binary Significance
of the Address Bit
Address Bit
System Manual
C79000-B8576-C199-03