Chapter 6 PLC Programming 139
• There are icons for nine data files in the
Data Files
area: Input (I), Output (O), Status (S2),
Timer (T4), Counter (C5), Control (R6), Integer (N7), and Bit (B3 & B10).
• If PLC latch and unlatch instructions are used in industrial control systems, it is possible
to dictate that an output device must turn on when a pushbutton is pressed and that the
same output device must turn off when another pushbutton is pressed.
• Placing the PLC on the run mode allows the PLC to start controlling the input/output
devices.
• Placing the PLC on the online monitor mode allows the programmer to see the operation
of a running PLC control system on the computer screen.
• Offline mode is the mode when the PLC ladder logic diagram can be created.
• Online mode is when the PLC program is downloaded into the PC.
• A method of testing the PLC system without actually closing or opening input
devices is to test the PLC in the forced condition mode.
• The force condition must be used with extreme caution.
• The seven commands for creating and printing PLC reports in RSLogix 500 software
found under the
File
menu are the following:
View,
Preview,
Report
Options,
Report
Preview,
Report,
Printer
Setup, and
Page
Setup.
Review Questions
1. How many output instructions can you place in series in a ladder logic diagram?
2. What processor type is used for the Allen-Bradley fixed
SLC 500 PLC with twelve 120 VAC input ports and eight
120 VAC output ports?
3. Which slot must be reserved for a processor in the modular Allen-Bradley PLC system?
4. Which file holds the main PLC ladder logic diagram?
5. What are the following PLC input instruction types: XIO and XIC?
6. What steps do you take to place an input or output instruction in forced mode?
7. Which data file holds the error messages?
8. Should you use the PLC force instruction in an industrial plant when assembly line
workers are present? Why or why not?
9. List the seven commands available for creating and printing.
10. Describe how to open and save a project.
Complete each of the following sentences with the correct word(s).
11. You must energize the ______ coil to close an XIC Latch/Unlatch contact.
12. Bit addresses B3:0 through B3:255 or ______ through ______ may be used for latch/
unlatch.
13. To latch or unlatch a contact, two ______ are used.
14. The PLC system can be tested without actually closing or opening input devices in the
______ mode.