Rockwell Automation 1769-SM2 Compact I/O DSI/Modbus Communication Module - Manual (Page 195)

Glossary-5
S
Scanner
A scanner is a separate module (of a multi-module controller) or a
built-in component (of a single-module controller) that provides
communication with modules connected to a network. See also
Controller.
Status Indicators
Status indicators are LEDs that are used to report the status of the
module, network, and drive. They are on the front of the module.
Z Zero Data
When communication is disrupted (for example, the controller is idle),
the module and drive can respond with zero data. Zero data results in the
drive receiving zero as values for Logic Command and Reference data. If
the drive was running and using the Reference from the module, it will
stay running but at zero Reference.