ControlLogix digital input modules share many of the same features and functions as their digital output siblings. There is, however, one difference—the diagnostic input module, which will be detailed in the following section.
Diagnostic input modules
A diagnostic input module (denoted by a D in the product catalog identifier) provides troubleshooting functionality that can detect when a wire is disconnected and can latch the value when an error occurs (used to diagnose intermittent issues). The diagnostic options are visible in the digital input module properties. The following screenshot illustrates the differences between a normal digital input module (on the left) and a diagnostic input module (on the right):
The following screenshot shows the contents of the additional Diagnostics tab that appears and allows the user to reset any latched diagnostic inputs...
