A system includes a programmable transmitter device (e.g., a PLD) connected to a programmable receiver device (e.g., another PLD) via a transmission medium for transmitting a high-speed data signal from the transmitter to the receiver. During a test mode of operation a low-speed communication link between the transmitter and receiver allows those devices to work together to transmit test signals having known characteristics from the transmitter to the receiver via the transmission medium, to analyze the test signals as received by the receiver, and to adjust at least some aspect of the system (e.g., equalizer circuitry in the receiver) to at least partly compensate for losses in the test signals as received by the receiver.