A built-in self-test circuit for use in testing a serializer/deserializer circuit includes a programmable transmit register that transmits data to the serializer/deserializer circuit having programmably varying characteristics. The built-in self-test circuit includes the transmit register that transmits data to the serializer/deserializer for processing into processed data, a receive register that receives the processed data from the serializer/deserializer, and an error detector that detects errors in the processed data.