The brain of the PLC that executes the stored program, performs arithmetic operations, and manages memory.
To understand where Webb and Reis's book fits in the landscape, let's compare it to other major PLC textbooks.
Unlike older versions that focused solely on relay ladder logic and the big three brands (Allen-Bradley, Siemens, Modicon), the updated 5th edition attempts to bridge the gap between classic PLC control and modern PC-based automation.
RAM or EEPROM used to store the user-written control logic, timer/counter presets, and the status of inputs and outputs. 3. Input/Output (I/O) Modules The brain of the PLC that executes the
Modular I/O cards allow field technicians to replace faulty channels or entire blocks without replacing the core CPU, minimizing industrial downtime.
On Goodreads, the book maintains a 4.3-star rating based on user reviews. Reviewers call it a "best book for plc" and praise its accessibility for students with no prior background. The platform shows 55% of users rating it 5 stars, with only 10% giving 1 star.
The book is rich with learning aids designed to reinforce understanding: RAM or EEPROM used to store the user-written
Modern PLCs feature built-in Ethernet ports and MQTT protocols to send operational data directly to the cloud for predictive maintenance and enterprise data analytics.
The scan cycle runs indefinitely while the PLC is in "Run" mode and consists of three distinct phases:
You are also part of a very large group of learners. Why? Because for over two decades, Webb’s textbook has been considered the "golden key" to understanding the brains of modern manufacturing. On Goodreads, the book maintains a 4
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Webb and Reis define the PLC as a solid-state, industrial computer designed specifically to operate in harsh environments (resisting dust, moisture, and heat) to monitor inputs and make logic-based decisions for output control. ResearchGate Logic Scanning : A fundamental principle detailed in the book is the Scan Cycle , which involves: Input Scan : Reading the status of all input devices. Program Scan : Executing the user-defined logic based on those inputs. Output Scan
Ultimately, Webb and Reis delivered a masterful introduction that has stood the test of time. While the automation industry has moved forward, the foundation they built remains as solid as ever—and for those just starting their journey into the world of programmable logic controllers, their book is still a wise place to begin.