ALP to interface 8086 processor with 8255 PPI to generate the square wave

; Assume the interface is connected over J4 of trainer
; This program generates a Square or Triangular wave at Xout or Yout
; The program can be executed in Stand alone or Serial mode
; Execute the program from memory location 2000H

                OUTPUT 2500AD
                ORG 2000H
                MOV AX,0000H
                MOV CS,AX
                MOV ES,AX
                MOV DX,0FFE6H           ;Initialise all 8255
                MOV AL,80H              ;ports as O/P ports
                OUT DX,AL

      START:              
               MOV AL,0FFH              ;start from FFH
                         
                MOV DX,0FFE0H           ;+ive going slope and      
                OUT DX,AL               ;output at port A & B
                MOV DX,0FFE2H
                OUT DX,AL
                CALL  DELAY
                MOV al,00H             ;set count
                                ;decrement data for
                MOV DX,0FFE0H           ;-ive going slope at
                OUT DX,AL               ;port A & B
                MOV DX,0FFE2H
                OUT DX,AL
CALL DELAY
                JMP SHORT START              ;repeat continuously
DELAY:          MOV  CX,094DH            ;Delay routine
SS:             LOOP SS
                RET
                END

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Rishabh Chatterjee

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