Heterogeneous physical media attachment circuitry for integrated circuit devices

An integrated circuit includes physical media attachment ('PMA') circuitry that includes two different kinds of transceiver channels for serial data 5 signals. One kind of transceiver channel is adapted for transceiving relatively low-speed serial data signals. The other kind of transceiver channel is adapted for transceiving relatively high-speed serial data signals. A high-speed channel is alternatively 10 usable as phase-locked loop ('PLL') circuitry for providing a clock signal for use by other high- and/or low-speed channels. A low-speed channel can alternatively get a clock signal from separate low-speed PLL circuitry.