Query regarding atc

I have passed both groups of IPCC in May 2011 and have completed 13 months of Articleship. Now due to Health problems, I am experiencing lots of Troubles and so, I feel that I cannot continue my articleship. I want to know about the ATC Scheme wherein One can pay Rs. 1000/- to the Institute and after submitting 1 Yr Articleship completion certificate, can obtain ATC Certificate. Suppose after doing so, I decide to re-join. Then will I have to Join the C.A Firm under whom I was Regd. as a Article or can join another Firm. Please reply if you are sure.