MOV  TMOD,#20H ;timer 1, mode 2 (auto reload)
          MOV  TH1,#-6   ;4800 baud rate
          MOV  SCON,#50H ;8-bit, 1 stop, REN enabled
          SETB TR1       ;start timer 1
AGAIN:    MOV  SBUF,#"A" ;letter "A" to be transferred
HERE:     JNB  TI,HERE   ;wait for the last bit
          CLR  TI        ;clear TI for next char
          SJMP AGAIN     ;keep sending A