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crez

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Joined: 24/10/2012
Location: Australia
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Posted: 04:18pm 13 Aug 2015

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my micromite+ is running a small test prog which spends about 3 seconds in sleep and then 3 seconds flashing an led. it responds to 2 settick interrupts happening about every 300ms. When I connect usb to pc it appears as COM5 but does not respond to ctrl-c issued by teraterm.

autorun on
baudrate 38400 - unchanged

I cant list the program because I cant access the chip

Any ideas?

G8JCF

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Joined: 15/05/2014
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Posted: 04:41pm 13 Aug 2015

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Use MMEdit to write and download your MMBasic programs

then then the source will be on your PC and you can back it up.

Peter

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Positron

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Joined: 09/08/2015
Location: Argentina
Posts: 15

Posted: 05:15pm 13 Aug 2015

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Just reset the mmite+ by disconnecting the power, installing a jumper between TX and RX pins of the console, finally restoring power. Your program will be erased but the OPTION AUTORUN will be disabled so you will get acces to the prompt and regain control.

crez

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Posted: 06:07pm 13 Aug 2015

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Positron, I didn't find this method in the latest manual. Is that pins 58 & 6 on the 64 pin chip?

In the mean time I attempted to reload the firmware (b23) using my pic-kit3, but it won't communicate either. After attempting that, it seem the led flashing program is not running anymore. Also it no longer is seen by windows as a valid usb device.
The only sign of life is 20MHz on the xtal, as seen by a DSO.

crez

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Posted: 06:10pm 13 Aug 2015

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Peter,
I agree, for next time. MMedit just hangs when trying to communicate at the moment.

TassyJim

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Posted: 06:50pm 13 Aug 2015

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If you had a failed attempt to reprogram it with a pickit3, your firmware is now corrupt which is why your USB port isn't working.

You will have to reprogram it with the pickit3 to get it back to the world of the living.

What version of Windows are you running?

Jim

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Grogster

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Posted: 06:52pm 13 Aug 2015

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It is possible that you have found a bug relating to the sleep command.
Geoff would be the guy to say for sure.

Sleeping the device will prevent access via CTRL+C by default. From manual(page 48, last of the notes for CPU SLEEP):

Quote CTRL-C on the console will not bring the chip out of sleep.

Smoke makes things work. When the smoke gets out, it stops!

crez

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Joined: 24/10/2012
Location: Australia
Posts: 152

Posted: 08:42pm 13 Aug 2015

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Thanks for the help, everyone, but pin 7 (MCLR) reads 1.0 ohm to gnd with everything disconnected from the board. I don't think there is any recovering from that

. The question now is did I stuff it while trying to fix it or was it the original problem? I now recall one of the last things I did last night was to issue a CPU 30 command in immediate mode.
What is the quickest way I can get a proper board to experiment on instead of this dogs breakfast I have hashed up?

Grogster

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Posted: 09:03pm 13 Aug 2015

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I can send you blank boards, kits or assembled module if you like - PM me if you want details etc. I have changed the CPU speed on the fly lots of times, and never had a problem, so I can say that this should not be the cause of your problem.

Smoke makes things work. When the smoke gets out, it stops!

srnet
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Joined: 08/08/2014
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Posted: 09:32pm 13 Aug 2015

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crez said Thanks for the help, everyone, but pin 7 (MCLR) reads 1.0 ohm to gnd with everything disconnected from the board

MCLR is the pin, where on some PICs, you apply a high voltage (VPP) to go into program mode. Edited by srnet 2015-08-15

$50SAT is Silent but probably still working.
For information on LoRa visit http://www.loratracker.uk/

JohnS
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Posted: 10:31pm 13 Aug 2015

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The only way I know to damage a pin (such as MCLR) like that would be hardware (such as putting high volts on it).

John

crez

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Posted: 02:12am 14 Aug 2015

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Perhaps I plugged the pickit3 programmer in while it was powered up. If the MCLR pin meets before the GND then there could be a significant voltage difference. I had the grounded cro probe attached to the MM and the programmer/PC supply is floating.

bigmik

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Posted: 02:51am 14 Aug 2015

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Hi Crez,

The cro probe may have been the issue.. If you plugged the GND anywhere but on the GND pin it could have destroyed your PIC chip

A good vid clip on Cro probes and blowing a test circuit can be seen HERE!!!

Regards,

Mick

Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<<

crez

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Posted: 12:26pm 15 Aug 2015

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Mick,
I have a large ground plane around my circuit where I was connecting the scope gnd. I'm pretty sure it didn't connect anywhere else.

Several times I have had a brief zap from the Antenna connector of a double insulated set-top-box or tv. This is a firm reminder that if your mains plug has only two prongs then there is no true ground there. I just measured the voltage on the USB shield from my laptop using the scope and it is peaking up to 120v. If I connected the PICKIT to the circuit while it was connected to the USB and the MCLR pin touched before the GND (very likely) then the MCLR pin would see that high voltage.

David

Positron

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Posted: 03:29pm 15 Aug 2015

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David (crez), if you suspect that you hace a floating neutral in your mains electrical installation, to be safe you should disconnect the power cord from your notebook when using USB connections with other independently powered devices, so the notebook is running on battery. This will effectively isolate your device.

Hope this helps.

bigmik

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Posted: 03:51pm 15 Aug 2015

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Hi Crez,

What happens if you forcibly short MCLR to 3v3? Or better still try a low value Resistor at first say start at 1k then drop down to 470R and 200R then 100R before trying a dead short as this could short your Power supply..

It is looking increasingly like the Pic has been killed by plugging the earth of cro probe onto the wrong section of the circuit.

Mick

Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<<

bigmik

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Posted: 03:54pm 15 Aug 2015

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Hi Crez,

I have had a rethink... Probably you wont be able to program the chip again if you short to 3v3 and that could be detrimental to your PK3 so DONT short to 3v3 and try to program it.. try a 1k ohm to 3v3

Mick

Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<<

crez

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Joined: 24/10/2012
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Posts: 152

Posted: 12:43am 16 Aug 2015

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Positron,
Yes, running the laptop on battery would isolate it from the mains and would probably have prevented the problem. I don't see how a floating neutral is relevant as there is no d.c. connection between the output of the laptop supply and the mains. Just out of curiosity I measured the voltage neutral to mains gnd and it was 0.7vac on my multimeter. That would be the voltage drop in the neutral back to the switchboard where the neutral is earthed and would vary depending on what loads are connected to the circuit at the time.

Mick,
I had given up on resurrecting the micro so I powered it up on a bench supply at 3.3v . It drew 100mA on the Vdd but when I connected the MCLR directly to 3.3v the current rose to 1.4A and the micro got hot. It's dead for sure!

In the future I will be sure to connect the pickit to the micro before connecting the USB so that the GND has a solid connection before it is powered up. Not having a GND on the board ( via scope or otherwise) would probably be a good precaution too. I should probably also check that the pickit is not applying more than 3.3v.

David

robert.rozee
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Joined: 31/12/2012
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Posted: 01:01am 16 Aug 2015

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crez said I just measured the voltage on the USB shield from my laptop using the scope and it is peaking up to 120v.

for any double-insulate mains appliance, it is not uncommon to measure 1/2 of the mains voltage at an exposed metal point (be it at the shaft of an electric drill, or one of the output terminals of a power supply).

HOWEVER, there is almost no current behind this voltage, it exists there merely because of capacitive coupling from the mains side of the device. having said this, "almost no current" can still damage an electronic component that is not protected!

while there is no electrical fault in the appliance, it is kind of a good idea when doing electronic experimenting to create a common ground situation for everything. this can consist of working on a static mat that connected via a 470k resistor to one of:
(1) the ground terminal on your soldering station,
(2) a 3-pin plug that has a lead running from the ground pin,
(3) if using a desktop computer, a ground from the metal case.

if using a laptop/netbook that is running from a mains adapter, it is highly likely that the computer will be floating. connect a lead from the metal shell of a USB plug, or the shell of a 15-pin VGA plug, or some other metal point that is joined to the chassis, back to your common ground point.

the goal is that everything metal should be tied together at the same potential, and that point then tied to the mains ground via a 470k resistor. the purpose of the resistor is to ensure that if a genuine ground fault does occur, that minimal current can flow. at 230v, a 470k resistor will only pass about 500uA.

cheers,
rob :-)Edited by robert.rozee 2015-08-17

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