.model small
.data
        PA EQU 0E880H
        PB EQU 0E881H
        PC EQU 0E882H
        CWR EQU 0E883H

        POSCYCLE DB 80h,8bh,96h,0a1h,0abh,0b6h,0c0h,0c9h,0d2h,0dah,0e2h,0e8h,0eeh,0f4h,0f8h,0fbh,0feh,0ffh,0feh,0fbh,0e8h,0f4h,0eeh,0e8h,0e2h,0dah,0d2h,0c9h,0c0h,0b6h,0abh,0a1h,96h,8bh,80h

        NEGCYCLE db 80h,75h,6ah,5fh,55h,4ah,40h,37h,2eh,26h,18h,12h,0ch,08h,05h,02h,01h,00h,00h,01h,02h,05h,08h,0ch,12h,18h,26h,2eh,37h,40h,4ah,55h,5fh,6ah,75h,80h

.code

        MOV AX,@DATA
        MOV DS, AX

        MOV AL, 80H
        MOV DX, CWR
        OUT DX, AL

        AGAIN:
                LEA SI, POSCYCLE
                MOV CX, 35
                POSVAL:
                        MOV AL, [SI]
                        MOV DX, PA
                        OUT DX, AL
                        MOV DX, Pb
                        OUT DX, AL

                        CALL DELAY
                        INC SI
                        LOOP POSVAL

                MOV CX, 35
                LEA SI, NEGCYCLE

                NEGVAL:
                        MOV AL, [SI]
                        MOV DX, PA
                        OUT DX, AL
                        MOV DX, PB
                        OUT DX, AL

                        CALL DELAY
                        INC SI
                        LOOP NEGVAL

                MOV AH, 06
                MOV DL,0FFH
                INT 21H

                CMP AL, 00
                JZ AGAIN
        INT 3H

        DELAY PROC
                PUSH CX
                MOV CX, 06H
                OUTER:
                        PUSH CX
                        MOV CX, 0FFFFH
                        INNER:
                                NOP
                                NOP
                                NOP
                                NOP

                                LOOP INNER
                                POP CX
                                LOOP OUTER
                POP CX
                RET
        DELAY ENDP

END