A serial communications protocol with optional and adjustable data link layer and physical layer features is provided. A logic design tool for designing circuits compliant with the protocol is also provided. Using the logic design tool, desired optional protocol features may be included to enhance circuit functionality and undesired optional protocol features may be omitted to conserve circuit resources. The logic design tool may include design aids related to retry-on-error timeout calculations, FIFO sizing, transmitter and receiver circuit parameters, and other design parameters. A user of the logic design tool can view information provided by the logic design tool's design aids and can make design selections.