Microchip TC32M Supervisory Circuit and Bootloader

[modifyit]

I'm trying to implement a supervisory circuit which acts as an external watchdog timer which resets my 16f877a chip if the program locks up.

In order for it to work the program on the 877a must strobe the TC32M every so often or the TC32M will reset the pic. Under normal operation everything works as it should.

I have a problem however when I try to program the chip with a bootloader. Durring the programing the TC32M does not see the required strobe so it resets the pic and the programing stops.

Anyone know any creative options to make the bootloader work with this supervisory circuit?

[Dave]

modifyit, I personally use the ADM690 or MAX690 supervisory ic in my designs because if the input pin is left unconnected or (tristated) the watchdog timer quits operation. This way during the bootloader initialization the port I have it connected to is also in a input or (tristate) mode so the bootload can take place. After which the port is programmed as an output and from then on the watch dog timer will have to be strobed atleast every 1.6 seconds before it will reset the micro and external circuitry. Try it, You'll like it....

Dave Purola,
N8NTA

[modifyit]

The MAX690 seems to be a nice solution, but the watchdog timeout is a little long at 1.6sec. I think I would prefer to use the TC32M if I can figure out a creative way to do it.

[mytekcontrols]

Just curious...
Any reason you're not using the PIC's internal watchdog and/or brownout detector?

[modifyit]

My project is working in a harsh enviroment which has caused issues with the microprocessor even with internal brownout and watchdog protection. So partially its out of necessity and partially belts and suspenders.

[modifyit]

Any other thoughts? I guess I could try and come up with a circuit that will monitor the rs232 chip to tell if it is programing and disconnect the mclr from the TC32M when that happens. I'm not positive how to do that tho.

Thanks again

[NavMicroSystems]

Any other thoughts?

How about using a 10F PIC as supervisory circuit?
(It would be fully programmable)

That's what I'm going to do on one of my current projects.

[modifyit]

Interesting thought, how would you suggest implementing the brownout protection portion of the 10F?

I guess I could make a 10F send a strobe out to reset the TC32M during a bootload.This may be a little excessive tho, not sure what I am going to do at this point.