Chapter 5 Applied Instructions API 07 The instruction WDT is used to reset the watchdog timer in a motion control module. If the scan time in a motion control module exceeds 200 milliseconds, the error LED indicator of the motion control module will be ON, and users will have to disconnect the motion control module. After the users connect the motion control module again, the module control module will judge its state according to the setting of the STOP/RUN switch. If there is no STOP/RUN switch, the module will stop running automatically. The points when a watchdog timer acts are as follows. The system is abnormal.
The execution of a program takes much time, and therefore the scan time is greater than the setting value in SR0. There are two ways users can use to improve the situation. 1. Using the instruction WDT Explanation O100 M102 WDT 2. Changing the value in SR0 (The default setting is 200 milliseconds.) T1 T2 Example Suppose the scan time is 300 milliseconds. After the program is divided into two parts, and the instruction WDT is inserted between these two parts, the time it takes to scan either the first part of the program or the second part of the program will be less than 200 milliseconds. The program is divided into two parts.
The time it takes to scan either the first part of the program or the second part of the program is less than 200 milliseconds. X0.0 WDT 150ms program The watchdog timer is reset. M102 The instruction WDT is executed when a condition is met. Users can make the instruction WDT executed only in one scan cycle by writing a program. They can use the pulse instruction WDTP. The default setting of a watchdog timer is 200 milliseconds. Users can set a watchdog timer by means of SR0. Additional remark 5-25 Instruction code Operand Function WDT P – Watchdog timer Pulse instruction 16-bit instruction (1 step) 32-bit instruction – 300ms program M102 150ms program