One aspect provides a programmable logic device. The device includes an input circuit for detecting a multi-level input signal and an output circuit. The input circuit includes: an input pin for receiving the multi-level input signal; first and second programmable voltage generators to generate, respectively, first and second multi-level voltage signals; a pair of comparators, each comparator having a first input coupled to the input pin and a second input coupled to a corresponding programmable voltage generator; and a logic gate coupled to the comparators, thereby facilitating the detection of the multi-level input signal based on outputs of the comparators. The output circuit includes a third programmable voltage generator to generate a third multi-level voltage signal, an output pin, and a voltage buffer coupling the third programmable voltage generator to the output pin, thereby facilitating the programmable logic device to output, over the output pin, the third multi-level voltage signal.