Multiplexed Key Matrix 
This keypad matrix converts a key press into a specific analog value that is related to the SnapCPU for processing. Keypad matrix consists of 16 uniquely identifiable keys. By communicating using an analog value, only a single SnapCPU pin is required to be allocated for communications.
The KodeKLIX Blockly plug-in includes a special coding block for accurately reading the buttons.
Power is connected to +v and the analog data representing the unique key press is available at one of the ADC connections.