of the MCS-51 Family, as listed below: Pin P3.0 P3.1 P3.2 P3.3 P3.4 P3.5 P3.6 P3.7 Name RXD TXD INT0 INT1 T0 T1 WR RD Alternate Function Serial input line Serial output line External Interrupt 0 External Interrupt 1 Timer 0 external input Timer 1 external input External Data Memory Write strobe Exte.