MS-DOS Interrupt Vector

[tcwong3]

I am writing a TSR program for MS-DOS 6.22 for trapping RS232 interrupt.

In order to do that I need to know interrupt vector for COM1 & COM2 (or 3 & 4).
For example the vector for keyboard interrupt is 0x09.

Can anyone help me on this?

Thanks in advanced.

 

[M!k]

these are the interrupt vectors (decimal):
#define COM2_VECT 11 /* COM2 */
#define COM1_VECT 12 /* COM1 */

and these are the interrupt numbers:
COM2 = COM4 --> IRQ3
COM1 = COM3 --> IRQ4

you'll find a list here:
https://bioscentral.com/misc/interrupts.htm


Mik

 

[albert22]

There is a DOS service to get and change the interrupt vectors.
Here is an example for the COM port:
com_irq db 4 ;COM port IRQ
save_ISR dw 0,0 ;saved interrupt vector

mov al,com_irq ;save COM interrupt vector
add al,8
mov ah,35h
int 21h
mov save_ISR,bx
mov ax,es
mov save_ISR+2,ax
pop bx
pop es

mov al,com_irq ;set new vector
add al,8
mov ah,25h
mov dx,offset COM_ISR
int 21h
--------------
restore_COM:
pushf
push ax
push dx
cli

push ds
mov al,com_irq ;restore interrupt vector
add al,8
mov ah,25h
lds dx,dword ptr save_ISR
int 21h
pop ds
.......
These routines are using services 25h and 35h of the DOS int21.
Hope that helps
K

 

[tcwong3]

Thank you very much. I will try it.