Books:

1. Gary Dunning, "Introduction Programmable Logic Controllers", CENGAGE Learning, 3rd Ed., 2006.
2. John R. Hackworth, Frederick D. Hackworth Jr., "Programmable Logic Controllers ", Pearson, 2004.
3. W.Bolton, "Programmable Logic Controllers", Elsevier, 4th Ed., 2006.

Useful links:

1. https://literature.rockwellautomation.com/
2. https://www.automation.siemens.com/