Circuitry detects properties of an accessory removably connected thereto via a multi-pole connector. The circuitry has first, second and third circuit terminals for coupling to respective first, second, and third poles of said connector, and has an output for providing evaluation values from which properties of the accessory may be derived. In the circuitry, first current sourcing circuitry is coupled to said first circuit terminal for providing a first current. A switch network comprises first, second, third and fourth switch network terminals, said first switch network terminal coupled to a reference potential, said second switch network terminal coupled to said second circuit terminal, and said third switch network terminal coupled to said third circuit terminal. Comparator circuitry provides a comparison signal, its first input terminal being coupled to said first circuit terminal. Second current sourcing circuitry having a monitor node coupled to said second comparator input terminal and an output node coupled to said fourth switch network terminal provides a second current to said switch network. At least one of said first current sourcing circuitry and said second current-sourcing circuitry is responsive to a digital control word for varying said first or said second current. Control logic is provided for operatively controlling the state of the interconnections of said switch network, for adjusting said digital control word in response to said comparison signal until a voltage at said first circuit terminal is equal to a voltage at said monitor node, and for supplying said adjusted digital control word associated with the state of the interconnections to said output as an evaluation value.