Two types of watchdog functionality are implemented for the Modicon M241 Logic Controller:
oSystem Watchdogs: These watchdogs are defined in and managed by the controller firmware. These are not configurable by the user.
oTask Watchdogs: These watchdogs are optional watchdogs that you can define for each task. These are managed by your application program and are configurable in EcoStruxure Machine Expert.
Three system watchdogs are defined for the Modicon M241 Logic Controller. They are managed by the controller firmware and are therefore sometimes referred to as hardware watchdogs in the EcoStruxure Machine Expert online help. When one of the system watchdogs exceeds its threshold conditions, an error is detected.
The threshold conditions for the 3 system watchdogs are defined as follows:
oIf all of the tasks require more than 85% of the processor resources for more than 3 seconds, a system error is detected. The controller enters the HALT state.
oIf the total execution time of the tasks with priorities between 0 and 24 reaches 100% of processor resources for more than 1 second, an application error is detected. The controller responds with an automatic reboot into the EMPTY state.
oIf the lowest priority task of the system is not executed during an interval of 10 seconds, a system error is detected. The controller responds with an automatic reboot into the EMPTY state.
NOTE: System watchdogs are not configurable by the user.
EcoStruxure Machine Expert allows you to configure an optional task watchdog for every task defined in your application program. (Task watchdogs are sometimes also referred to as software watchdogs or control timers in the EcoStruxure Machine Expert online help). When one of your defined task watchdogs reaches its threshold condition, an application error is detected and the controller enters the HALT state.
When defining a task watchdog, the following options are available:
oTime: This defines the allowable maximum execution time for a task. When a task takes longer than this, the controller will report a task watchdog exception.
oSensitivity: The sensitivity field defines the number of task watchdog exceptions that must occur before the controller detects an application error.
To access the configuration of a task watchdog, double-click the Task in the Applications tree.
NOTE: For more information on watchdogs, refer to EcoStruxure Machine Expert Programming Guide.
