An integrated circuit includes physical media attachment (“PMA”) circuitry that includes two different kinds of transceiver channels for serial data 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 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.