// AVR pseudo code
// DDRB.1 = 1;     // make output
// PORTB.1 = 1;    // SOURCE current
// PORTB.1 = 0;    // SINK current
// DDRB.2 = 0;     // make input
// key = PINB.2;   // read level ( needs external or internal pull-up )

// 8051 pseudo code
// P1.1 = 0;       // SINK current
// key = P1.2;     // read level ( needs external pull-up )