;send master network address then data byte
   ORL SCON,#(UART_MARK_ADDRESS) ; setb TB8
   MOV SBUF,#MASTER_ADDR
WAIT_SEND1:                      ; jnb TI,$
   MOV A,SCON
   ANL A,#(UART_SEND_DONE)
   JZ  WAIT_SEND1
; send data byte
   ANL SCON,#NOT(UART_MARK_ADDRESS OR UART_SEND_DONE) ; clr TB8 and clr TI
   MOV SBUF,#DATA_BYTE
WAIT_SEND2:                      ; jnb TI,$
   MOV A,SCON
   ANL A,#(UART_SEND_DONE)
   JZ  WAIT_SEND2
   ANL SCON,#NOT(UART_SEND_DONE) ; clr TI