The paper addresses the digital controller structure problem for the closed loop stability of a feedback digital control system subject to finite word length (FWL). A new method of maximizing the stability subject to perturbations in the digital controller implementation is proposed. The approach is based on structured perturbation theory in an l(1) framework, and unlike some previous approaches, can be simply extended to consider closed loop nominal performance and closed loop robust performance and stability. The method is demonstrated with application examples.