Determine the Pulse Transfer Function and State Space Model of the DC Motor 
References
Books
Katsuhiko Ogata - Discrete-Time Control Systems (Second Edition, Prentice Hall)
M. Gopal - Digital Control and State Variable Methods (Second Edition, Tata McGraw-Hill)
Video Lectures
Click here for NPTEL Lecture on Digital Control Systems
("Lecture 1: Motivation for using Z-transform, Lecture 3: Pulse Transfer Function, Lecture 4: Pulse Transfer Functions of Closed Loop Systems", Module 2: Modeling Discrete Time Systems by Pulse Transfer Function)
("Lecture 1: Introduction State Variable Model", Module 7: Discrete State Space Models)