1) A field that specifies the source of the clock for the transmit clock input/output (CLKX) pin. At reset, MCM = 0. This bit is stored in the serial port control register (SPC) and the time-division multiplexed (TDM) serial port control register (TSPC). 2) A bit within the synchronous serial port control register (SSPCR) that determines whether the source signal for clocking synchronous serial port transfers is external or internal.