The modules must be addressed individually so that the bus communication is possible. Addressing follows the standard Modbus addressing rules.
Each module has an address ranged 1 to 255. It acts as a slave, i.e. it is waiting until being addressed by the process station, and then responds back. Address of 0 is reserved for software address setting, it can not be used for regular communication. The master (process station) does not have an address.
The default module address (factory settings) of every module and room unit is 1. The I/O modules must be readdressed at the commissioning phase or prior to it. It is convenient if the designer assigns the module addresses in the drawings for easier reference. If he or she does not do this, the addressing plan must be set up by the software engineer. The engineer must know the address assignment not later than the software project is being designed, and the input and output variables are defined.
The modules may be addressed with gaps, it is not necessary that the addresses physically follow each other on the bus.
It is highly recommended to define the addresses as soon as in the system topology drawings and in the shop drawings, so that the modules may be referred to and there are no ambiguities. If the modules connected to one bus are located in more panels, it is recommended to allocate a separate addressing space for each panel so that there is a reserve for future expansions.
RM1 addresses 1…50
RM2 addresses 51…100
RM3 addresses 101…150
At the commissioning time it is useful to attach a label with module address to the cable tray above the module, or a removable sticker to the module front.