Random hardware reset issue

Jonathan

Hi All,

I am having a problem with the Prop on my 'bot. It is randomly resetting the Prop. Looking at the reset line using a scope, I see the voltage drop to 0 for about40uS, then ramp back up to 3.3V over another 40uS or so.

I have a prop clip hard soldered to the bot. When I plug in the programming cable, the problem goes away. I have re-soldered all the connections, checked the grounds·and saw no improvment.

Next thing to try from this end is a new Prop chip. I know I have one around here somewhere...

Any ideas on how to track this down would be great.

Thanks!

Jonathan



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Erik Friesen

Not sure what your problem may be but I added 1K resistors between all my communication lines going to my programmer and it made everything a lot less sensitive. Sometimes I think the programmer can drag down the reset line when unpowered or in a transistion state of being plugged in.

deSilva

I have found no circuit for the PropClip, but it certainly uses an cap for differenciating the DTR signal as all other circuits. As this signal is somewhere hidden in the USB protocol I see no point of intervention...

But I should exchange the Clip rather than the Prop!

Fred Hawkins

put a switch on the reset line to the propclip?

Jonathan

Hmm...

I replaced the Prop, and the issue *seems* to have gone away. At least, it has been 20mins with no reset, and I was getting > one per min before.

So, how did I damage the Prop? I do a LOT of hot swapping i.e. program, pull the cable out and test, plug back in, rinse and repeat. Is hot swapping OK? Can I add any protection to minimize the possibility of damage? I have been working with this Prop in this way for a couple of months.

Thanks for the help!

Jonathan

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Jonathan

Drat!

Just after I wrote the above, I did get a random reset. It still seems much better, but it's back to the drawing board.

I'm hoping it is not the Prop Clip. It is hard soldered onto the board, and I only have one replacement which I would rather keep available for other Prop projects.

Is it possible that the internal 5k pullup is not enough? Could I add an external one of 4.7 to 10k?

Jonathan

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Phil Pilgrim (PhiPi)

This is a known problem with the USB circuitry when it's not plugged into a USB port. Put a 2.2K pullup from A30 to Vdd, and the problem should go away. Here's a link that explains why:

····http://forums.parallax.com/showthread.php?p=651731

The pullup isn't the best solution, since it's actually being used to power the FTDI chip. A better solution would be buffer circuitry between the FTDI chip and the Prop, so current doesn't backfeed through the FT232R's serial I/O pins.

-Phil

Jonathan

Phill,

Thanks! It's been an hour now and the pullup seems to be working.

Now however, I wonder why this problem never showed up until now. I have been using the same setup for a couple of months. Why would it suddenly become such a recurrent problem?

Anyway, thanks very much!

Jonathan

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Jonathan

Double Drat!

Still having the problem. Argh!

Fred, I'm going to try your idea and see if it isolates it to the Prop clip.

Any other ideas folks?

Jonathan

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Phil Pilgrim (PhiPi)

Jonathan,

Even with the pullup on A30, if your program should ever pull A30 low and return it high, the Propeller will reset. Also, I'm not sure entirely sure the 2.2K resistor is stiff enough to power the FT232R adequately. You may want to try a 1K instead. In any event, the switch that Fred recommended will isolate the problem — and even solve it, if you don't mind turning it on and off when necessary. But as I alluded to before, the pullup is a pretty sketchy workaround...

-Phil

Jonathan

Phil,

I will try a 1k pullup. However, I am still having problems understanding why this issue would creep in to an existing project that has been OK for a couple of months. I am beginning to think it is the Prop clip. It now seems to be an on and off issue, so I can't be *sure* that the pullup is helping. It sits stable for a while, then will crash a bunch. I keep thinking power supply, but the 3.3V supply shows no sag when the Prop resets. Any other ideas of areas to check? I have been probing the grounds, but find no high resistance. I have decoupling caps sprinkled around and the ground is pretty much a star pattern.

Is there a definitve answer on hot swapping? Could I have damaged something that way? It just seems like somehow I must have done something to upset a previously stable situation.

Thanks a ton for your help, this project has come to a halt until I can track down and squash this bug.

Jonathan

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Phil Pilgrim (PhiPi)

Jonathan,

Are you sure your program can't be toggling A30 and/or A31? Another possibility is noise pickup on the FT232R's DTR output line. If this line isn't being driven adequately (i.e. if the chip isn't powered), it's possible that an induced voltage spike on the reset transistor's input cap could cause the transistor to switch long enough to reset the prop. A stiffer pullup on A30 may or may not help with this. If not, it's hard ot know what to recommend. A pulldown resistor on DTR would certainly help, but any mods to the Prop Clip itself are almost certain to involve major microsurgery.

-Phil

Jonathan

Phil,

I don't *think* I can be toggling A30/31. The pin assignments have been stable for quite a while, and all the program is doing when it crashes is using fullduplexserial to monitor incoming commands from an EB500 bluetooth module. I just took a look through and don't see any reason for A30/31 to be toggled.

Hmmm, one thing that I just found is that I am initializing the BS2_functions routines with 30/31. I am not actually uising the commands at the moment, so I just commented it out. As the only functions that use the pins initialzed are the debugin/out commands and I am not using them, it doesn't seem a likely culprit.

It bothers me that it is seemingly random, and it makes it tough to figger out what is the problem.

Thanks a TON for the help!

Jonathan

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