Watchdog circuit

QWE4562009

Watchdog circuit [Copy link]

A problem with the watchdog circuit

QWE4562009

Is the microcontroller's watchdog signal a level-reversing signal, a square wave? The last time it was high, the next time it was low? Can't the watchdog be given a high or low level at a fixed time?

dcexpert

External watchdogs are usually edge-triggered, as long as a trigger signal is provided. Please refer to the chip manual for details.

machinnneee

Look at the description and yes, alternating high and low levels are used to feed the dog.

wsmysyn

The previous company made a pin2pin compatible chip of 706 series.

This only requires a level inversion of the WDI pin within 1.6s, a rising edge or a falling edge, to clear the Watchdog counter inside the 706 chip to 0. There is a 10kHz RC, 14-bit counter inside, which overflows when it counts to 16384. Of course, the 10kHz RC is not very accurate, and it is about right to adjust it to 9kHz to 11kHz.

The microcontroller program can use the timer to make a timing, such as a 1s timing. When the MCU counts for 1 second, the IO port is reversed. It looks like a square wave and cannot be fixed high or low. It is an edge trigger, not a level trigger.

If the dog feeding signal is not generated within 1.6s, WDO will change from high to low, pulling the MR pin low, thereby pulling the reset pin low and resetting the system. When the reset is valid, the chip will automatically clear the wdg timer, WDO will become invalid, and MR will also become invalid, and the reset pin status will not be deadlocked; after the reset is valid for 200ms, the reset becomes invalid, the MCU can be restarted, and the 706 continues to work normally.

QWE4562009

dcexpert posted on 2020-12-2 21:41 The external watchdog is usually edge-triggered, as long as the trigger signal is provided. Please refer to the chip manual for details.

This means that the level of the signal needs to be flipped.

dcexpert

QWE4562009 posted on 2020-12-3 18:07 Then it means that the level flip signal is required

When the level is flipped, doesn't it provide a rising/falling edge signal?

damiaa

QWE4562009 published on 2020-12-2 18:59 The microcontroller feeding signal is a level inversion signal, is it a square wave? The last time it was high level, the next time it was low level? It is not possible to give the watchdog a high level regularly...

It's OK to give a square wave. It's equivalent to two flips. That's fine. One more is fine. Without it, it won't work.

QWE4562009

damiaa posted on 2020-12-4 12:33 QWE4562009 posted on 2020-12-2 18:59 The microcontroller feeding signal is a level inversion signal, is it a square wave? The last time it was high level, the next...

To put it bluntly, the level still needs to be flipped.