ANALOG IO CONTROLLER IN DEVICENET

Dear sir, Actually i want to develop an ANALOG IO CONTROLLER in the devicenet netork.I am using 4 analog input and 4 analog out put channels with

120v ac as input , i am stepping down this voltage to 3.3v that can be given as an input for my A/D converter inside my controller.Does the analog voltage 120vac needs to step down to the required operating voltage of the analog pins inside my controller or else do i need to calculate the exact voltage between 0 to 120vac in this ANALOG IO CONTROLLER modules that can be fed as input to the controller analog pins. Can you please explain me how an analog i/o controller works with respect to 0 to 120 vac input voltage in the device network. With Regards, Vasu