Troubleshooting
For many of the latest generation controllers, there is often a marque that can display messages that provide very descriptive troubleshooting hints directly on the device.
The latest revs of the Allen Bradley CompactLogix and ControlLogix families of PLCs have a small marque that displays the PLC name, the program running on the PLC, and the status and IP address of each Ethernet port. If a mapped Ethernet module stops responding the marque will display an I/O fault. The Productivity PLC series from Automation Direct provides a similar multi-line LCD text screen for diagnostic information.
Some newer PLCs have integrated full-color LCD displays and keypads so that maintenance staff and integrators can scroll through very descriptive fault and warning messages and configure some settings. The Siemens S7-1500 PLC series offers this type of display and keypad right on the front of the CPU module.