Modbus station address

Modbus defines valid station addresses in the range 1 to 247. A Modbus slave only responds to telegrams that contain its own address. Address 0 is not a valid station address. It is used for broadcast telegrams to all stations. These are not answered. Addresses 248 to 255 are reserved.

The Tc2_ModbusRTU library defines further collective addresses. This enables a station to respond to several addresses.

TYPE MODBUS_UNITID :
(
    MODBUS_UNITID_BROADCAST       := 0,
    MODBUS_UNITID_ALLVALID        := 256, (* response on address 1..247 *)
    MODBUS_UNITID_ALLBUTBROADCAST := 257, (* response on address 1..255 *)
    MODBUS_UNITID_ALL             := 258 (* response on address 0..255 *)
);
END_TYPE