Modbus: Item address changes to 6 digits.

Modbus addressing is made up of 2 components. The first part is the first digit of the address which identifies what type of memory you are addressing. For example, a 4 indicates a holding register where a 1 would indicate an Input coil. The second part is the register offset which we pad with 0's to support the larger memory space of newer devices.

This means that if your device uses 4 digit addressing for holding registers (40001) the Modbus drivers will pad what you type with 0's to make it look like a 5 digit address (400001). This is still the same address; the driver knows that it is requesting Modbus Holding register 1 and makes the appropriate request.