www.logiccircuit.org

Dear Forum members,

first thanks for this great tool, it is awesome.

I've one question (I'm not an electronic engineer)

A MCU has a watchdog signal (~Pulse). I'd like to use the WDS to set certain states via logic (e.g. CAN Transmitters turned on as long as WDS is okay).

Therefore the WDS has to be changed from pulse to (1). I thought using a Monoflop may be a way to do that. Can someone give me a hint how to realize a monoflop in logic circuit?

To a further extend - if the WDS signal from the MCU fails, the Watchdog itself triggers a short pulse to (reset, do something else). This signal should then be used to disable the capability to switch on the transmitters, e.g. if it happens more than 2 times during a power cycle (First time may be a test, second time may be caused by a failure,). In this case you don't want that this MCU is again "recognized" as up and running and is disabled to transmit (at least for a certain time period unit it is "~sure" that it does not fail again immediately.

I appreciate hints

Kind regards,

Tobias

Hi Tobias,
You've used a lot of acronyms that I have no idea about. Maybe you can just formulate what circuit do you need and i will try to help you.
Regards,
Eugene

Eugene!

Thanks for your reply.

A MCU = Micro Controller (some CPU)
Watchdog = a signal periodically send by the CPU whenever a task is completed or as long the internal power supply is okay (e.g. each tasks has at the end a codeline "send alive()". If one tasks gets stuck (endless loop) -> the watchdog signal fails. In most cases, this triggers a reset of the my-Controller.

a) the MCU creates a periodical signal (e.g. 0 to 3.3V). I want to change this signal to a continuing 1 as long as the periodic signal is coming, and switching to 0 if it not anymore received (e.g. after 10milliseconds).

I thought that a Monoflop may be a solution to change the pulse to a "constant" 1 bit state.

When it is 1 I enable e.g. the CAN BUS transmitter.
When it is 0 I disable e.g. the CAN BUS transmitter.

At the end I need also to watch out that the MCU has no hard failure and does not continuously/repeating "lock up" due to a e.g. SW failure. Therefore I may accept a reset a single time, but not twice. If it happens more than 2 or 3 times, the CAN BUS transmitter stays disabled.

I hope I explained it better

-Tobias

I can only think of a counter with reset signal bringing it to 0. When there is no reset signal then counter counts up to some value and this is the indication of a loop. The reset signal is your watchdog.