From the article:

move.l #$dff000,a0 ;Base for hardware registers

lea save(pc),a1 ;Get the system

move.w #$4000,intena(A0) ;from the AMIGA

Crude, although perfectly fine in practice. The system-friendly way is to call the function exec.library has for the purpose, Disable()[0].

0. http://amigadev.elowar.com/read/ADCD_2.1/Includes_and_Autodo...