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'[PIC][OT] Crappy doc, software, assumptions'
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. 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.
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.
 Another story about crappy product from an Asian supplier on Ebay. A new speed controller had a bad 555 timer and possibly bad FETs
At 01:33 PM 4/1/2012, Joe Wronski wrote:
>o Crappy software - MPLAB X should have known the target board had
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 Reid <planet.eon.net> dwayner
Trinity Electronics Systems Ltd Edmonton, AB, CANADA
(780) 489-3199 voice (780) 487-6397 fax
Custom Electronics Design and Manufacturing
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.
Because the target board was being powered by the ICD3. In the original MPLAB, I recall a dialog box that reported VDD and VPP.
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