A programmable logic device (“PLD”) includes high speed serial interface (“HSSI”) circuitry that can support several high speed serial (“HSS”) standards. Examples of the standards that can be supported are XAUI, InfiniBand, 1G Ethernet, FiberChannel, and Serial RapidIO. The HSSI circuitry may be partly programmable to support these various standards. In some cases control may come from the associated PLD core circuitry. Also in some cases some of the interface functions may be performed in the PLD core circuitry.