  This article studies the zero-error feedback capacity of {\em causal}
discrete channels with memory. First, by extending the classical zero-error
feedback capacity concept, a new notion of {\em uniform zero-error feedback
capacity} $ C_{0f} $ for such channels is introduced. Using this notion a tight
condition for {bounded} stabilization of unstable {noisy} linear systems via
causal channels is obtained, assuming no {channel} state information at either
end of the channel.
