Ivan,

If you aren't using Transmit Interrupts you should first check to see if the UART is available to transmit a character by checking the LSR. The example below also doesn't check Clear to Send;

uart_rdy_loop:
    mov   dptr,#LSR
    movx  a,@dptr
    jb    acc.5,uart_rdy_loop
uart_is_rdy:
    mov   dptr,#THR
    movx  @dptr,a

Since you are not using Receive Interrupts a polling routine that waits for available data (and also doesn't check modem signaling) could look like;

uart_rx_loop:
    mov   dptr,#LSR
    movx  a,@dptr
    jnb   acc.1,uart_rx_loop   
uart_rx_avail:
    mov   dptr,#RHR
    movx  a,@dptr

regards,
p