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'[PICLIST] (PIC): Possible miswiring of my board...'
2001\01\23@113628 by Ken Robertson

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Last night, I was trying other things to simply see that my PIC was working,
since I lacked the MAX232 to work with my 877.  I noticed that nothing was
working (turning on a LED, writing something to eeprom), so I think I might
have wired it wrong, but don't know how it should be.  Could someone maybe
spot a problem and tell me?

I'm using the 877 with the Warp-13 programmer, CCS compiler, and PICProto64
board from meLabs.  For power, it has 11v coming in from a AC-DC adapter,
regulated with a 7505 with a 10uf cap on the incoming power line and a .1uf
cap on the regulated line.  I have checked it, and regulated power is going
through the board fine.

The crystal is where I think it might go wrong.  The crystal is from Jameco
and is the CY20.  It is placed with a 22pf cap on either side.  Is 22pf
right for a 220mhz crystal?  I mainly question this because the Jameco
website/catalog just says "Series" in the impedance column.

I am really new to PICs (haven't even gotten my first one working :).  I'm
going to order a book, so that might help.  Mainly need some schematics and
parts lists for a 877, so I know what is right for this chip.

Thanks a lot for any help you can offer,
 Ken

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2001\01\23@114858 by Richard Sloan

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If you are using a 220Mhz clock on it I would think this is your issue.

R.

-----Original Message-----
Is 22pf
right for a 220mhz crystal?  I mainly question this because the Jameco
website/catalog just says "Series" in the impedance column.


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2001\01\23@115259 by Bob Blick

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> website/catalog just says "Series" in the impedance column.

Bingo. You want "parallel" crystals for the PIC.

-Bob

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2001\01\23@120731 by Ken Robertson

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Ahh, I guess I should get one then. :)  Do the crystals have a particular
polarity?  Ohh, and 20mhz, not 220.  My error.

Also, I noticed on the board that I am missing a resistor that connects +5v
to MCLR, that it another problem.  What resistor should I use?  I put a 22k
one there, but I guess now it isn't working because of that crystal.

Thanks!
 Ken

{Original Message removed}

2001\01\23@122634 by M. Adam Davis

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You could connect mclr directly to +5 as well - it just has to be high or
the pic will not run (ie, it is in a state of reset whenever low)

Any resister below, say 470k ohm will work.  You can use higher, but it
won't make any significant difference on current draw, and capacitive
effects of the circuit board start to make a difference in how fast the
circuit is reset, wakes up, etc.

The reason most people use a resistor is so that you can still ground the
mclr without shorting the power supply to induce a reset.  If you never
plan on reset the circuit this way it's still a good idea to follow this
practise, though you could just hook mclr directly to +5 and be fine.

-Adam

Ken Robertson wrote:
{Quote hidden}

> {Original Message removed}

2001\01\23@135056 by Bob Ammerman

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> Also, I noticed on the board that I am missing a resistor that connects
+5v
> to MCLR, that it another problem.  What resistor should I use?  I put a
22k
> one there, but I guess now it isn't working because of that crystal.

The resistor is absolutely necessary.

Series specced crystals with often work, but with reduced accuracy.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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2001\01\23@162854 by David VanHorn

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At 09:04 AM 1/23/01 -0800, Ken Robertson wrote:
>Ahh, I guess I should get one then. :)  Do the crystals have a particular
>polarity?  Ohh, and 20mhz, not 220.  My error.

No polarity.

220 MHz is a bit optimistic though.

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2001\01\24@004948 by Anand Dhuru

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Mark, everything does seem all right beside the crystal. Are you SURE it is
220 MHz? If it is, its way out of boundary; the 877 is to be used at a
maximum frequency of 20MHz, anything lesser would also work. Try using a
crystal of 20Mhz or less.

Cheers,

Anand.
{Original Message removed}

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