Prior to connecting any modules to a Profinet IO capable (Siemens) PLC, a GSDXML configuration file needs to be installed in your PLC programming software (i.e. STEP 7 or TIA Portal). The GSDXML file contains, among other things, the definition of memory size required when connecting a module to a Siemens PLC with Profinet IO. When assigning an individual module to a PLC, you decide what memory address to use. The GSDXML file stipulates that each module requires 64 bytes of input data from the module to the PLC and 64 bytes of output data from the PLC to the module. When assigning an individual module to a PLC, you decide what physical PLC memory address to use as the beginning of these 64-byte blocks.
In all of the charts showing module data registers and their assigned function, for Profinet IO these are indicated as “Byte 0, Byte 1,…Byte 32”, etc. These are offsets from the starting address in the Siemens PLC memory assigned by the Siemens programming software when the module was installed into the network. For example, if a module’s inputs are installed beginning at %IB256, then from our charts, the data for “Byte 6 and Byte 7” would be at addresses %IB262 and %IB263 respectively.