; interrupt vector (memory from 00000h to 00400h) 
; keeps addresses of all interrupts (from 00h to 0ffh). 
; you can add new interrupt or modify existing interrupts. 
; address of interrupt M is stored in vector at offset M * 4, 
; for example: interrupt 10h is stored at offset 10h * 4. 
; first goes the offset, then segment (total of 2 bytes). 

; for more information refer to "global memory table" in c:\emu8086\documentation. 

; note: this is simplified example, it is not recommended to make changes to it 
; and run it on the real computer, especially it is not recommended to replace disk 
; processing interrupts because this may cause data loss and other instability problems. 


name "custint"


org 100h

start:

; set video mode to 3 - 16 color 80x25 
mov ah, 0
mov al, 3
int 10h


; set es to "0000": 
mov ax, 0
mov es, ax
; calculate vector address for interrupt 90h: 
mov al, 90h
; multiply 90h by 4, store result in ax: 
mov bl, 4h
mul bl
mov bx, ax
; copy offset into interrupt vector: 
mov si, offset [test1]
mov es:[bx], si
add bx, 2
; copy segment into interrupt vector:     
mov ax, cs
mov es:[bx], ax


int 90h    ; test newly created interrupt. 

; wait for any key press: 
mov ah, 0
int 16h


int 20h     ; halt execution. 





; interrupt 90h starts here: 
test1: pusha  ; store all registers. 

; make sure data segment is code segment: 
       push cs
       pop ds

; set segment register to video memory: 
       mov     ax, 0b800h
       mov     es, ax

; print message, each character is written as 
; a word, high byte is color and low byte is 
; ascii code: 
      lea si, msg      ; load offset of msg to si. 
      mov di, 0        ; point to start of the screen. 
print:
      cmp [si], 0      ; if "0" then stop. 
      je stop
      mov bl,  [si]    ; read ascii code from msg. 
      mov bh, 0f1h     ; set colors: white background, blue text. 
      mov es:[di], bx  ; write to vidio memory. 
      add di, 2        ; go to next position on screen. 
      inc si           ; next char. 
      jmp print
stop:
      popa  ; re-store all registers. 
      iret  ; return from interrupt. 

msg db "test of custom interrupt!", 0