Generation of rectangular wave using DAC interface

We write a program for the generation of rectangular interface of Digital to Analog Converter (DAC) interference:

 Let us consider a problem solution in this domain. The problem states that: To get unipolar output, J1 is shorted to J2 on the interface. To display the waveform on a CRO connect pin 1 of connector P1 to CRO signal pin, and pin 2 of connector P1 to CRO ground pin.

The program is stated as below.

; FILE NAME DAC_TO_RECT.ASM
ORG C100H
X DW 00FFH ; ‘OFF’ time is proportional to this value
Y DW 00C0H ; ‘ON’ time is proportional to this value

ORG C000H
PA EQU D8H
PB EQU D9H
PC EQU DAH
CTRL EQU DBH
MVI A, 88H
OUT CTRL ; Configure 8255 ports
LOOP: LHLD Y
XCHG
LHLD X ; Now DE contains 00C0H and HL contains 00FFH

MVI A, 00H
OUT PA ; Sending 00H to DAC through the Port A
CALL DELAY ; Generation of delay proportional to the contents of HL.

XCHG ; Now HL contains 00C0H
MVI A, FFH
OUT PA ; Sending the FFH to Digital to Analog Converter through Port A
CALL DELAY ; Generation of delay proportional to the contents of HL
JMP LOOP
; Subroutine to generate a delay proportional to contents of HL

DELAY: DCX H
MOV A, H
ORA L
JNZ DELAY
RET