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'[PIC][OT] Crappy doc, software, assumptions'
2012\04\01@153031 by Joe Wronski

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I haven't done much PIC work since leaving $JOB over 2 years ago.  Recently, I've been getting back into it.   The subject line describes today's experience.
I had bought an Olimex PIC-P28 dev board as a platform for some quick projects.  One such project came up where I wanted to generate a PWM signal with a PIC to test some motor speed control FETS[1].  I made up a program that output a PWM signal, and it reflected the PWM signal on the LED, and a button cycled the duty cycle in 10% steps from 0 to 100%.  I used HiTech C Lite with MPLAB X and an ICD3, and observed the output with my old Tektronix 453 bought around 1988, I'd guess.
It was working nicely, so today, I soldered a header on the Olimex board to extend the PWM output to a radio shack breadboard (we used to call them continental specialties boards).  I connected it up, powered it on, and nothing.  Unplugged breadboard, still nothing.  Connected it to ICD, and try to debug, and MPLab tells me the device ID is 0.   I ran Debugger Self Test and it passed.
Long story short, the pins I had selected on the Olimex board are on a semi documented "grtound bus", so I had shorted the board's VCC to GND.    Looking at the Olimex manual, the pictures show a hint of shading that should have told me this.  The manual mentions GND bus, but does not specify where it is.   It also mentions Vcc bus, so I better locate that.

So:
o Crappy Doc.   Olimex could do a better job
o Crappy software - MPLAB X should have known the target board had shorted supply.
o Crappy assumptions - I assumed my wiring was OK.

Fortunately, the board survived and moving the header allowed me to test FETs.

Joe W


[1] Another story about crappy product from an Asian supplier on Ebay.  A new speed controller had a bad 555 timer and possibly bad FETs

2012\04\01@235218 by Dwayne Reid

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At 01:33 PM 4/1/2012, Joe Wronski wrote:

>o Crappy software - MPLAB X should have known the target board had
>shorted supply.

Question: How could MPLABX possibly know about a shorted power rail on the target board?  All it knows is that it can't communicate with the target chip, which could be any of a dozen (or more) different problems..

Not being confrontational - I'm genuinely curious.

dwayne

-- Dwayne Reid   <spam_OUTdwaynerTakeThisOuTspamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax
http://www.trinity-electronics.com
Custom Electronics Design and Manufacturing

2012\04\02@141510 by Joe Wronski

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On 4/1/2012 11:52 PM, Dwayne Reid wrote:
> At 01:33 PM 4/1/2012, Joe Wronski wrote:
>
>> o Crappy software - MPLAB X should have known the target board had
>> shorted supply.
> Question: How could MPLABX possibly know about a shorted power rail
> on the target board?  All it knows is that it can't communicate with
> the target chip, which could be any of a dozen (or more) different problems.
>
> Not being confrontational - I'm genuinely curious.
>
> dwayne
>
Because the target board was being powered by the ICD3.  In the original MPLAB, I recall a dialog box that reported VDD and VPP.

Joe W

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