An electronic module for use in a printer consumable unit includes a first input and output (I/O) port adapted connected to an external contact, and a second I/O port connected to the external contact. Circuitry controls the electronic module and responds to read memory commands and write memory commands received through the external contact on the I/O ports. A memory stores data. A third port is connected to the external contact and adapted to source current. The circuitry is initially configured to send and receive data through the first I/O port. The circuitry tests the functionality of the first I/O port by directing the third port to source current and drive the external contact to a predetermined voltage, and read a voltage received by the first I/O port in response to sourced current. If the circuitry determines the first I/O port is not functioning correctly based on the read voltage, the circuitry will send and receive data through the second I/O port.