A co-ordinate system is simply a plot which helps to picture the vectors well. Reference frames helps in analysing the vectos and solving the kinematics.
All reference frames can be expressed in the form of a co-ordinate system, but a co-ordinate system is something which has application in many other matters.
Physically speaking, Reference frame is an object with respect to which the dynamical properties of the object under observation is measured. It is based on the concept of inexistence of something absolute. A co-ordinate system is selected for the convenience of understanding the vectors and solve the dynamics between them by simple algebraic analysis. In fact both are very much the same but not the same. A reference of frame need not have co-ordinate system. the system is for the easiness of solving vectors. The co-rdinate system in a reference frame is to map the dynamic situation of ibjects with respect to it.