The same testing equipment can be used to test devices operating under different protocols. Where the testing protocol is slower than the native serial protocol of the high-speed serial link connecting the device processor to the component to be tested, the link may be adapted to carry the lower speed testing protocol. This may be accomplished by adding low-speed buffers to the circuits of the serial link, or the serial link may have a native low-speed protocol in addition to its high-speed protocol connections may be made to the pathways for the native low-speed protocol, or the testing protocol may be impressed on top of native low-speed protocol. Where the driver of the device being tested has limited number of pins, the test mode can be controlled by applying power to different power supply input pins.