This application provides apparatus and methods for initiating tests in an interface circuit without using inputs of the interface circuit dedicated to initiating the tests. In an example, a test mode interface circuit can include a voltage comparator configured compare a first voltage to a second voltage, a ripple counter configured to count pulses from a processor when the voltage comparator indicates that the first voltage is greater than the second voltage, and wherein the test mode interface circuit is configured to provide a test mode enable signal and an indication of the a desired test mode an interface circuit that includes the test mode interface circuit.