disp_data:  ;** proc * ouput to display one symbol to current position
        ;* arg * R4 - symbol's code
        mov A, R4   ; move symbol's code from R4 to Acc
    ; write code to data register of display
        mov R0, A
        mov DPTR, #7FF6h    ; await wite-ended-flag set
    bf1:movx A, @DPTR
        anl A, #80h
        jnz bf1
        mov DPTR, #7FF5h    ; writing symbol's code to data register
        mov A, R0
        movx @DPTR, A
    ret