PUBLIC F2250_
F2250_ PROC
                cmp     al, 10h
                jz      loc_40689
                mov     al, 3
                iret
        loc_40689:
                mov     ax, di
                cmp     al, 2
                jz      loc_40697
                mov     al, 3
                iret
        loc_40697:
                mov     al, 1
                iret
F2250_ ENDP

PUBLIC F2251_INSTALL_CRITICAL_HANDLER
F2251_INSTALL_CRITICAL_HANDLER PROC
                push    ds
                mov     edx, offset F2250_
                push    cs
                pop     ds
                assume ds:nothing
                mov     ax, 2506h       ; AH = 25 = SET INTERRUPT VECTOR. AL = 06 = vector number
                mov     cl, 24h         ; ?
                int     21h             ; DOS - SET INTERRUPT VECTOR
                                        ; AL = interrupt number
                                        ; DS:DX = new vector to be used for specified interrupt
                pop     ds
                ret
F2251_INSTALL_CRITICAL_HANDLER ENDP
