does the 180 days start from the entry date, or does it start from the issue date?

i have an F type multiple entry visa. The duration of each stay is 180 days. My issue date was August 19.2011, my entrance date was September 15.2011, My visa has no expiration date. So my question is does the 180 days start from the entry date, or does it start from the issue date? And if it starts from the Issue date, what can i do? Are there penalties? Or should i just high tailit for the american embasy