My check engine light went off after a year?

I have a 1998 isuzu trooper and the engine light has been on for the past year and recently it went off. I was having problems with my battery and the alternator. I had to have the battery jumped several times and I noticed that the check engine light went out during this time. I just replaced the battery and alternator and the engine light is still off. Not that I'm complaining that its off or anything I was just wondering if it takes the ECM awhile to reprogram itself and that's why the light hasn't come back on yet.