In a previous lesson we explained the purpose of the watchdog timer. In this lesson, we will expand that lesson a little further and demonstrate the function of the watchdog timer. We are going to modify a previous program that contains a properly executed jump instruction such that it creates a condition called an infinite loop. An infinite loop condition causes the watchdog timer to time out, which in turn causes the PLC to go into Stop mode. We explain how a properly executed jump instruction should be written to avoid this condition.
In the previous lesson, we had a program that contained a comparator instruction and it properly executed our jump instruction. We then changed that instruction to a field input. When we forced that input to true in the simulator, we managed to put our program in an infinite loop, causing a Stop ...
In some cases you may need to flash a bit in your PLC program. Let’s say that you have an HMI that is not capable of flashing an alarm notification. In that case, you may use the PLC program and one of a number of ways to flash a bit. You can then use that bit on the HMI to indicate a flashing al...
In the previous lesson we talked about the different ways to generate timing pulses or flashing bits within your PLC program. Also, in other lessons, some time ago, we discussed how to generate pulses using timers. In this lesson, we are going to recap how to create these pulses and work with the...
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