Error Detection, Types, and Management

Error Management

The controller detects and manages three types of errors:

oExternal errors

oApplication errors

oSystem errors

This table describes the types of errors that may be detected:

Type of Error Detected	Description	Resulting Controller State
External Error	External errors are detected by the system while RUNNING or STOPPED but do not affect the ongoing controller state. An external error is detected in the following cases: oA connected device reports an error to the controller. oThe controller detects an error with an external device, for example, when the external device is communicating but not properly configured for use with the controller. oThe controller detects an error with an output. oThe controller detects a communication interruption with a device. oThe controller is configured for an expansion module that is not present or not detected. oThe boot application in Flash memory is not the same as the one in RAM.	RUNNING with External Error Detected Or STOPPED with External Error Detected
Application Error	An application error is detected when improper programming is encountered or when a task watchdog threshold is exceeded.	HALT
System Error	A system error is detected when the controller enters a condition that cannot be managed during runtime. Most such conditions result from firmware or hardware exceptions, but there are some cases when incorrect programming can result in the detection of a system error, for example, when attempting to write to memory that was reserved during runtime, or when a system watchdog time-out occurs. NOTE: There are some system errors that can be managed by runtime and are therefore treated like application errors.	BOOTING → EMPTY

Type of Error Detected

Description

Resulting Controller State

External Error

External errors are detected by the system while RUNNING or STOPPED but do not affect the ongoing controller state. An external error is detected in the following cases:

oA connected device reports an error to the controller.

oThe controller detects an error with an external device, for example, when the external device is communicating but not properly configured for use with the controller.

oThe controller detects an error with an output.

oThe controller detects a communication interruption with a device.

oThe controller is configured for an expansion module that is not present or not detected.

oThe boot application in Flash memory is not the same as the one in RAM.

RUNNING with External Error Detected

STOPPED with External Error Detected

Application Error

An application error is detected when improper programming is encountered or when a task watchdog threshold is exceeded.

HALT

System Error

A system error is detected when the controller enters a condition that cannot be managed during runtime. Most such conditions result from firmware or hardware exceptions, but there are some cases when incorrect programming can result in the detection of a system error, for example, when attempting to write to memory that was reserved during runtime, or when a system watchdog time-out occurs.

NOTE: There are some system errors that can be managed by runtime and are therefore treated like application errors.

BOOTING → EMPTY

NOTE: Refer to the M218 PLCSystem Library Guide for more detailed information on diagnostics.