AssemblyLanguage/7_2_3.asm at master · Siarnold/AssemblyLanguage · GitHub

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NAME EX7_2_3

DATA SEGMENT
    ADDRESS EQU 0280H
    KEEP_IP DW ?
    KEEP_CS DW ?
    DAT DB 0FFH
    OUTPUT DB '  ',0DH,0AH,'$'
DATA ENDS
STACK SEGMENT PARA STACK
      DB 100 DUP(?)
STACK ENDS
CODE SEGMENT
  ASSUME CS:CODE,DS:DATA,ES:DATA,SS:STACK
MAIN PROC FAR
START: MOV AX,DATA
       MOV DS,AX
       MOV ES,AX
; protect interrupt vector
       PUSH DS
       MOV AH,35H
       MOV AL,0BH
       INT 21H
       MOV KEEP_IP,BX
       MOV KEEP_CS,ES
       POP DS
; change interrupt vector IRQ3
       PUSH DS
       MOV DX,OFFSET INTR
       MOV AX,SEG INTR
       MOV DS,AX
       MOV AH,25H
       MOV AL,0BH
       INT 21H
       POP DS
; initialize 8259
       IN AL,21H
       AND AL,0F7H
       OUT 21H,AL
; initialize 8255
    MOV AL,10100000B; method 1, A input
    MOV DX,ADDRESS+3
    OUT DX,AL
    MOV AL,00001101B
    OUT DX,AL

; main
MAIN0:
    MOV AH,0; keyboard read in
    INT 16H
    CMP AL,0EH ; break when 0EH
    JNE ENDD
    JMP MAIN0
ENDD:
; restore interrupt vector
    CLI
    PUSH DS
    MOV DX,KEEP_IP
    MOV AX,KEEP_CS
    MOV DS,AX
    MOV AH,25H
    MOV AL,0BH
    INT 21H
    POP DS
    MOV AH,4CH
    INT 21H
    RET
MAIN ENDP

INTR    PROC FAR; interrupt vector
    STI
    NOT DAT
    MOV AL,DAT
    MOV DX,ADDRESS
    OUT DX,AL
    MOV AL,20H
    OUT 0A0H,AL
    OUT 20H,AL
    IRET
INTR ENDP
CODE ENDS
END START