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'[PIC] Weird voltages on RB-pins (PIC16F886)'
2007\06\28@064859 by Rikard Bosnjakovic

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part 1 1542 bytes content-type:text/plain; charset=ISO-8859-1; format=flowed (decoded 7bit)

See the attached schematic. It is a simple cable-tester for a couple
of adapters I built. The tester is supposed to work like this:

A loop puts RB7, RB6, ..., RB3 high (in that order), one at a time.
RA0-RA4 are the inputs that checks if the actual pin is OK or not (a
high RB7 should give a high RA0, RB6->RA1, and so on).

When I did one cable-pin at time as described above, the tester worked
as it should. One red LED and one green LED got lit for my reference
cable. The problem with testing one pin at a time is if accidentally
switched two wires in the cable. Then the green leds would - ofcourse
- not be lit, but I thought it would be nice to see which of the wires
that are wrong.

So I rewrote the code to test all five wires for each of the
PORTB-pins. That is, RB7 high -> test all of RA0, RA1, ... and turn on
the green LEDs, move to RB6, check all RA's again, etc. I cannot see
anything wrong in my code, and it's probably not wrong either.

What's really confusing me is that when RB7, RB6 and RB5 are high
(still one at a time), my multimeter shows only ~0.6volts on those
pins. When RB4 and RB3 are high, I get ~4.7 volts and those wires are
tested accordingly.

All analog inputs are turned of (ANSEL and ANSELH are cleared), the
TRIS-regs are correct, comparators are disabled, vreg is off, pull-ups
are disabled. The board is double-checked, no broken copper traces and
no double-traces.

Anyone got a fair guess of what could be wrong?


--
- Rikard - http://bos.hack.org/cv/


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2007\06\28@070357 by Marcel Birthelmer

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My first guesses would have to be that you're maybe exceeding the
specced max current for the chip/ports? Also, I think it might be
considered bad practice to connect multiple LEDs to the same resistor,
but I might be wrong about that.
Regards,
- Marcel

2007\06\28@074618 by Jan-Erik Soderholm

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Rikard Bosnjakovic wrote:

> See the attached schematic.

Use one resistor/LED.
And where are the values of all components ?

> All analog inputs are turned of (ANSEL and ANSELH are cleared), the
> TRIS-regs are correct, comparators are disabled, vreg is off, pull-ups
> are disabled.

Hard to verify for us who can't see the code...

Write the shortest possible test-case that shows the problem
and post that (not your full app, just a short code that shows
the problem...)

Jan-Erik.

2007\06\28@080933 by Alan B. Pearce

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>> See the attached schematic.

OK

>Use one resistor/LED.

Well, he doesn't need to if the leds are multiplexed, which would be OK in
this application, so only one LED is on at a time. Even flicker would be
acceptable as the LEDs are scanned - shows that the unit is operating, and
not stalled.

>And where are the values of all components ?

That is the more important thing, and what micro are you using ???? - OH it
is in the subject line, but not on the circuit - bad move.

2007\06\28@083339 by Kevin Timmerman

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Are you using an ICD2 to program the PIC? If so, make sure to use the
Program menu in MPLAB, not the Debug menu. If the chip is programmed
with the debug executive, it will take control of RB6 & RB7 (program
clock and data). Also make sure LVP is not enabled, that would disable RB5.



>What's really confusing me is that when RB7, RB6 and RB5 are high
>(still one at a time), my multimeter shows only ~0.6volts on those
>pins. When RB4 and RB3 are high, I get ~4.7 volts and those wires are
>tested accordingly.

2007\06\28@090716 by Rikard Bosnjakovic

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part 1 919 bytes content-type:text/plain; charset=ISO-8859-1; format=flowed (decoded 7bit)

On 6/28/07, Kevin Timmerman <spam_OUTlistsTakeThisOuTspampcmx.net> wrote:

> Are you using an ICD2 to program the PIC? If so, make sure to use the
> Program menu in MPLAB, not the Debug menu. If the chip is programmed
> with the debug executive, it will take control of RB6 & RB7 (program
> clock and data). Also make sure LVP is not enabled, that would disable RB5.

I'm using an ICD2-clone. Project->Build configuration (in MPLAB) is
set to "release", and LVP is off.

I forgot to include the code in the original post, so I'm attaching it here.

> Use one resistor/LED.
> And where are the values of all components ?

Only one LED is on at a time, so there's no need to waste board-space
by adding a resistor per LED. The LED-resistors (R2 and R3) are 220
ohms, all other resistors (pull-downs + MCLR) are all 10k each.


--
- Rikard - http://bos.hack.org/cv/


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2007\06\28@093423 by Ariel Rocholl

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Kevin's question is whether you use the ICD2 as a programmer or as a
Debugger. This is unrelated to the build mode.


2007/6/28, Rikard Bosnjakovic <.....rikard.bosnjakovicKILLspamspam@spam@gmail.com>:
{Quote hidden}

> -

2007\06\28@094132 by Ariel Rocholl

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I do not see in your code you disabling comparators, as per the datasheet:


MOVLW H'7' ;Turn off

MOVWF CMCON0 ; comparators



2007/6/28, Ariel Rocholl <.....forosKILLspamspam.....arocholl.com>:
{Quote hidden}

2007\06\28@094206 by Ariel Rocholl

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I do not see in your code you disabling comparators, as per the datasheet:


MOVLW H'7' ;Turn off

MOVWF CMCON0 ; comparators


2007/6/28, Ariel Rocholl <@spam@forosKILLspamspamarocholl.com>:
{Quote hidden}

2007\06\28@095746 by Ariel Rocholl

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Sorry for the added noise, I was looking at PIC16F688 not 886. The previous
code doesn't seem to be required for disabling comparator in the 886 (I was
working with 16F688 yesterday, probably the cause of mistake - eyes read
what they want to)

2007/6/28, Ariel Rocholl <spamBeGoneforosspamBeGonespamarocholl.com>:
{Quote hidden}

>

2007\06\28@101301 by Rikard Bosnjakovic

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On 6/28/07, Ariel Rocholl <EraseMEforosspamarocholl.com> wrote:

> Kevin's question is whether you use the ICD2 as a programmer or as a
> Debugger. This is unrelated to the build mode.

Sorry. I'm using the ICD2 as a programmer. For debugging, I only use
the simulator.


--
- Rikard - http://bos.hack.org/cv/

'[PIC] Weird voltages on RB-pins (PIC16F886)'
2007\07\03@030016 by Rikard Bosnjakovic
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Just for the record, the problem is now "solved".

For some reason, RA0-RA2 did not work as inputs. They interfaced bad
with any output-port on the 16F887. I found this out by manually
"hijacking" the datalines and cross coupled the (not) intended ports,
and found that test #1-3 did not work under any circumstance when
connected to RA0-2, but flawlessly when connected elsewhere. Tried to
change the IC in case it was damaged, but I got the same weird
behaviour on other chips as well.

So, I moved RA0-3 to RC1-3. Works as a charm, but I have no clue as to
why RA0-2 didn't work as inputs, despite comparators/vrefs/analogs etc
turned off.


--
- Rikard - http://bos.hack.org/cv/

2007\07\03@064940 by Brent Brown

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I have a project using a PIC16F886. In my initialisation routine I set bit ADON = 0
(in ADCON0) to turn the A/D converter off. According to the datasheet ADCON0 = 0
on reset state anyway, but I have a funny feeling that I had problems with digital
inputs until I did that (my memory not too accurate).

On 3 Jul 2007 at 9:00, Rikard Bosnjakovic wrote:

{Quote hidden}

> --

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