HELP! PIC18F8722 Port F Input Problem

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GaryI Contact options for registered users 's Avatar (by Gravatar) posted on
February 19, 2008, 11:51 am
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Hi,



I'm using the 18f8722.  What I've noticed is that when I power up the
device and try to read Port F, I do not get anything back from pin 7
until after a few seconds of waiting. The circuit is fine, and the
port f pin 7 works fine on some hardware and this problem occurs on
other.  There's some kind of pic hardware issue with the functionality
of using pins 5/6/7 on port f.  I've done some testing and debugging
by moving lines to different pins but I've noticed that there's some
'correlation' between pins 5/6/7 on portf.



It all points towards a silicon issue possibly with the pic and has
yet to be reported by Microchip.  There's no info on the Silicon
Errata datasheets.



Help greatly appreciated!



Regards,




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BobW Contact options for registered users 's Avatar (by Gravatar) posted on
February 19, 2008, 7:47 pm
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Re: HELP! PIC18F8722 Port F Input Problem



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You need to be absolutely certain that you're meeting valid Vil and Vih on
all the inputs. If you haven't already done so, read the datasheet
carefully.

Bob



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GaryI Contact options for registered users 's Avatar (by Gravatar) posted on
February 20, 2008, 12:23 pm
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Re: HELP! PIC18F8722 Port F Input Problem


Hi,

Thanks for the reply.

As I've mentioned the hardware is setup correctly.

Any ideas?

GaryI Contact options for registered users 's Avatar (by Gravatar) posted on
February 20, 2008, 12:24 pm
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Re: HELP! PIC18F8722 Port F Input Problem


all are ok.....

so now?

Scott Seidman Contact options for registered users 's Avatar (by Gravatar) posted on
February 20, 2008, 1:55 pm
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Re: HELP! PIC18F8722 Port F Input Problem


snipped-for-privacy@34g2000hsz.googlegroups.com:

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What does this mean?  It works on some ucontrollers, but not on others, or
it works with some circuits on the same controller, but not all??


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GaryI Contact options for registered users 's Avatar (by Gravatar) posted on
February 20, 2008, 3:27 pm
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Re: HELP! PIC18F8722 Port F Input Problem


there are several boards the pic18f8722 is used on - and the delay
from "power-on to read" on poft f pin 7 'RF7' on one board is
different to another -

i.e.

a) on one board i hold a sw connected to RF7 and it takes about 10
secs before i get a correct read from pin 7,

b) on there boards theres no problem at all i perss the sw on RF7 and
read what i expect instantly,

c) whilst on another board which has an 8772, i hold a sw connected to
RF7 and it takes about 5 secs before i get a correct read from pin 7,

There a several boards which use various pics i.e. 2550, 452, but only
the 8772 seems to have this behaviour.

regards



Scott Seidman Contact options for registered users 's Avatar (by Gravatar) posted on
February 20, 2008, 4:24 pm
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Re: HELP! PIC18F8722 Port F Input Problem


snipped-for-privacy@e6g2000prf.googlegroups.com:

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I'm still having a hard time understanding.  Is this a "power-on-to-read"
problem, or a general slow read on port F?



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Spehro Pefhany Contact options for registered users 's Avatar (by Gravatar) posted on
February 21, 2008, 4:54 am
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Re: HELP! PIC18F8722 Port F Input Problem


On Tue, 19 Feb 2008 03:51:52 -0800 (PST), the renowned GaryI

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Do you have a pull-up or pull-down resistor? Have you configured the
port pins as digital inputs using ADCON1?  Have you verified that
ADCON1 is set correctly using a debugger?


Best regards,
Spehro Pefhany
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GaryI Contact options for registered users 's Avatar (by Gravatar) posted on
February 21, 2008, 10:35 am
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Re: HELP! PIC18F8722 Port F Input Problem


Read my message.... I connect directly to pin RF7 on the pic!!!!!
there's no pull downs up or anything else for that matter.... ALL and
i mean and know ALL registers are setup CORRECTLY!

Basically when the pic is powered theres a delay before i see anything
directly on that pin - as detailed in post dated '20 Feb, 15:27'

This pic is only couple of years old since design - looks like a
possible silicon issue!

Regards,


Scott Seidman Contact options for registered users 's Avatar (by Gravatar) posted on
February 21, 2008, 5:02 pm
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Re: HELP! PIC18F8722 Port F Input Problem


snipped-for-privacy@o77g2000hsf.googlegroups.com:

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What is the spec for this property?  If there is none, then you can't
design a system that counts on it.  You might look into any supervisory
chips that are in your system as well.


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