Provided is programmable circuit for interfacing with a field device. The circuit includes only one analog-to-digital converter (ADC) configured to receive from the field device one from the group including a current signal and a voltage signal. The received one signal has frequency shift keying tones (FSK) superimposed thereon, the ADC being configured to extract information from the received one signal and the FSK tones simultaneously. Also included is only one digital-to-analog converter configured to drive an output signal to the field device, the output signal (i) including one from the group including a current signal and a voltage signal and (ii) being summed with an FSK-modulated signal.