An integrated circuit (e.g., a programmable integrated circuit such as a programmable microcontroller, a programmable logic device, etc.) includes programmable circuitry and a channel of high-speed serial data signal interface (e.g., transceiver) circuitry. To facilitate enabling the integrated circuit to support any of many possible different high-speed serial communication protocols, the channel is hard-wired to include a parallel data bus of fixed width for exchanging parallel data with the programmable circuitry. Regardless of the protocol being implemented, the full width of this bus is always used. A portion of the programmable circuitry is programmed to convert data between the block width and a group width, which can be different from the block width and which is used for the data elsewhere in the integrated circuit.