Topic: DMD0262

Help File Version: 2.9.4.37

Configuring the Hardware Watchdog Timer

All of the Do-more CPUs contain a hardware watchdog timer that is used to put the CPU into a safe mode if the operating system ever stops running for more than 2 seconds. Configuring the desired mode of operation for the hardware watchdog time is done through the following two system-defined BIT locations:

 

$HwWatchdogMode (ST24) - Hardware Watchdog Timer Mode

 

If this System BIT is OFF the CPU will execute up to 10 warm-reboot attempts in an effort to return to RUN mode. Each time this process happens the CPU will do the following:

 

    • add an entry to the System Log noting the time the reboot occurred
       

    • the System Bit $WatchdogReboot (ST13) will also be set ON to indicate that a hardware-watchdog-induced reboot of the CPU has occurred
       

    • the value in $WatchdogReboots (DST385) value will be incremented by 1

 

If this System BIT is ON, or the value in $WatchdogReboots (DST385) is greater than 10, the CPU will NOT execute a warm-reboot; it will remain in the shutdown state with all eight of the LEDs glowing red. A power-cycle is required to get the CPU to return to Program mode.

 

Caution: disabling the Hardware Watchdog Timer is ONLY used when debugging problems with the operating system. You should not use the System BIT or the DIP switch to disable the Hardware Watchdog Timer unless directed to do so by the technical support personnel at AutomationDirect or Host Engineering.

 

$DisableHwWdog (ST25) - Enable / Disable Hardware Watchdog Timer

 

If this System BIT is OFF the hardware watchdog timer is enabled, and will operate according to the state of $HwWatchdogMode (ST24)

If this System BIT is ON the hardware watchdog timer is disabled, meaning that the hardware will not do anything if the operating system stops operating.

 

Note: if the hardware watchdog timer is disabled, and the operating system stops responding, the reset line on the backplane will be asserted, which will cause the I/O modules in the base to revert to their reset state, which typically is OFF for discrete outputs, a value of 0 for analog outputs, the CTRIO / CTRIO2 modules will transition out of RUN mode, and ERM / ERM100 modules will write their remote outputs to OFF or to 0 as appropriate.

 

Note: DIP switch #2 can also be used to disable the hardware watchdog timer. Follow this link for details on the DIP switches on the Do-more CPU.

 

See Also:

System Setup and Maintenance Overview
 

Changing the On-board Battery
 

Configuring the Hardware Watchdog Timer
 

LED Definitions
 

Mode Switch Position Definitions
 

DIP Switch Definitions
 

Communication Port Pinouts
 

Configuring the On-board Ethernet Port

 

Related Topics:

Do-more CPUs use a Software Watchdog Timer to put the CPU into Program mode if the CPU scan time exceeds a preset time limit.