Hackworth, J. R., & Hackworth, F. D. (2004). Programmable logic controllers: Programming methods and applications. Merrill, Pearson Education.

Hackworth, John R., and Frederick D. Hackworth. Programmable Logic Controllers: Programming Methods and Applications. Upper Saddle River, N.J. : New Delhi,IN.: Merrill, Pearson Education, 2004.

Hackworth, John R., and Frederick D. Hackworth. Programmable Logic Controllers: Programming Methods and Applications. Merrill, Pearson Education, 2004.