;;; RS-485 SERIAL COMMUNICATIONS.;;; Modes:;;; (1) Wait for address (REN = 1, T0 = 0, SM2 = 1);;; (2) Wait for data    (REN = 1, T0 = 0, SM2 = 0);;; (3) Send data        (REM = 0, T0 = 1)SER_ADDR equ 11110111b;;; All addresses should have the same number (7) of bits set.SetPort:   mov SCON, #11000000b ;;; Serial comm: 8 bits, no parity, 1 stop bit.      clr PS   clr RCLK   clr TCLK   mov A, TMOD   anl A, #00001111b   add A, #00100000b ;;; Timer 1: baud rate timer.   mov TMOD, A   mov TH1, #-3         ;;; Baud rate: 19200 baud.   setb TR1   clr TB8   clr RI   clr TI   setb ESretSetRx: ;;; Set mode for "Wait for address"   clr T0   setb SM2   setb RENretSetTx: ;;; Set mode for "Send data"   clr REN   setb T0retgetchar:   RecvLoop:      mov R0, #SP_RI      acall Pause      mov A, SBUF   jnb SM2, RecvData      cpl A      anl A, #SER_ADDR   ;;; A = SER_ADDR & ~SBUF      jnz NoMatch         clr SM2         ;;; if (A == 0) Set mode for "Wait for data";      NoMatch:   sjmp RecvLoop   RecvData:retputchar:   mov SBUF, A   mov R0, #SP_TI   acall Pauseret