Iowa v. Tovar, 124 S.Ct. 1379 (March 8, 2004) (trial court must inform unrepresented defendants of nature charges against him, right to counsel regarding plea, and range of allowable punishments for plea to be "knowing and intelligent,"; trial court does not need to inform accused that viable defense will be overlooked, or that he will lose opportunity to obtain independent opinion on whether it is wise to plead guilty).
http://laws.lp.findlaw.com/us/000/02-1541.html