; INT8 Demo - Revised 10/97
        ; Copyright 1996, 1997, John Lockwood

;====== Variables ===================

        oldv    DD  ? ; Old Vector (far pointer to old interrupt function)

        count   DW  0 ; Interrupt counter (1/18th second)
        scount  DW  0 ; Second counter 
        mcount  DW  0 ; Minute counter

;====== Main procedure =========================================

main    proc    far
        ..

        ; ---- Install Interrupt Routine-----

        call Install       


        ; ---- Main Body of Program (print count values) -----

showc:  MOV AX,mcount       ; Minute Count
        ..
        call pxy

        MOV AX,scount       ; Second Count
        ..
        call pxy

        mov ax,count        ; Interrupt Count (1/18th sec)
        ..
        call pxy

        MOV AH,1
        INT 16h             ; Check for key press 
        JZ showc            ; (Quit on any key)


        ; ---- Deinstall Interrupt Routine-----

        Call DeInst         ; Restore original INT8

        ..
main    endp

;====== Helper Function =========================================

pxy     proc near  ; Prints Text on Screen 
        ..          
pxy     endp

;====== Install Interrupt =========================================

Install proc near       ; Install new INT 8 vector
        PUSH ES

        MOV AL,8        ; INT = 8
        MOV AH,35h      ; Subfunction = Read Vector
        INT 21h         ; DOS Service

        MOV WORD PTR Oldv+0,BX
        MOV WORD PTR Oldv+2,ES

        MOV AL,8        ; INT = 8
        MOV AH,25h      ; Subfunction = Set Vector
        MOV DX,offset myint  ; DS:DX point to function
        INT 21h         ; DOS Service

        POP ES
        RET
Install ENDP

;====== Deinstall Interrupt =========================================

DeInst  proc near       ; Deinstall Routine 
                        ; (Reinstall old vector)
        ..

        MOV DX,word ptr Oldv+0
        MOV DS,word ptr Oldv+2

        MOV AL,8        ; INT = 8
        MOV AH,25h      ; Subfunction = Set Vector
        INT 21h         ; DOS Service
        ..
        RET
DeInst  endp

;====== ISR Code ===============================================

myint   proc near

        push DS         ; Save all registers
        push AX

        MOV AX,CS       ; Load default segment
        MOV DS,AX

        pushf           ; Call Orig Function w/flags
        call oldv       ; Far Call to existing routine


        INC count       ; Increment Interupt count
        CMP count,18
        JNE myintd

        INC scount      ; Next second 
        MOV count,0
        CMP scount,60
        JNE myintd

        INC mcount      ; Next minute
        MOV scount,0

myintd: POP AX          ; Restore all Registers
        POP DS

        IRET            ; Return from Interrupt 
myint   endp

;===============================================================