An integrated circuit on a system board is used, for example, in a digital audio device (such as a DVD or A/V receiver). The integrated circuit includes a digital-to-analog converter and the system board may include circuitry to mute the analog output of the device under certain predefined conditions. Because it may not be known in advance by the designer of the integrated circuit whether the circuit is activated by a signal in a high state (polarity) or a low state, the integrated circuit includes a detector which detects and stores the required polarity. When it is necessary for the circuit to be activated, the detector provides a signal of the correct polarity.