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PICList Thread
'ra4 on 16F84 inoperable'
1999\03\05@130534 by Stuart Meier

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Pin ra4 in a 16F84 application doesn't seem to work as an output in my app
(just turns on a test led)

I have checked...
   Set ra4 as an output in TRISA
   Not set as Tock1 in OPTION bit 5
   Not a faulty chip (programmed another f84 with the same code = same
fault)
   Not the code (worked fine when swapped with ra3 - but still no output on
ra4)

I'm a bit of a newbie, so it may well be something obvious I shouldn't have
overlooked.

Any suggestions, warmly received

Stuart Meier

1999\03\05@143939 by Peter Schultz

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This a open drain type. It will required pull-up resistor.

Peter Schultz
<spam_OUTschupetTakeThisOuTspamdvp.com>
DVP Inc.
3430 Ocean View Blvd. Unit A
Glendale, CA
(818) 541-9020
Fax: (818) 541-9423

>Pin ra4 in a 16F84 application doesn't seem to work as an output in my app

1999\03\05@145346 by spare

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> Pin ra4 in a 16F84 application doesn't seem to work as an output in my app
> (just turns on a test led)

Stuart,

RA4 is an open-collector output. If you want it to behave like the
other port A outputs, attach a pullup resistor to it (4.7K?)

Alternatively, if you just want to flash an LED, connect RA4 to the
cathode, and connect the anode to +5V (via a suitable resistor). Then,
driving A4 *low* will illuminate the LED, (I think).

Cheers,
Ben

1999\03\05@145355 by Andy Kunz

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At 06:05 PM 3/5/99 -0000, you wrote:
>Pin ra4 in a 16F84 application doesn't seem to work as an output in my app
>(just turns on a test led)
>
>I have checked...
>    Set ra4 as an output in TRISA
>    Not set as Tock1 in OPTION bit 5
>    Not a faulty chip (programmed another f84 with the same code = same
>fault)
>    Not the code (worked fine when swapped with ra3 - but still no output on
>ra4)
>
>I'm a bit of a newbie, so it may well be something obvious I shouldn't have
>overlooked.

Look at the diagram on the data sheet for pin RA.4.

You need a resistor to tie it to Vcc.  It's the odd pin on the PIC - only
one side of the transistor is tied in (to ground).

Andy

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    \    |   |    /          Andy Kunz
     \   /---\   /           Montana Design
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1999\03\05@150913 by Matt Bonner

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Stuart Meier wrote:
>
> Pin ra4 in a 16F84 application doesn't seem to work as an output in my app
> (just turns on a test led)
>
PortA.4 is an open drain output - you need to put a pull-up resistor on
it.  To use it with an LED, use a 330 ohm resistor from the PIC pin to
5V and put the LED to ground.  A "1" to the pin will turn the LED off
and a "0" will turn it on.

--Matt

1999\03\05@150923 by Adam Bryant

picon face
Check your datasheet.  The RA4 pin is an "open collector" output.  Insert
a resistor between the PIC RA4 pin and the LED with its other end
connected to your +5v source (size the resistor appropriately to avoid
overdriving the LED) and you should see the expected results.

       +5v
       |
       |
       Res
       |
       |
RA4 ----|---LED-------GND

Adam Bryant (age 0x23)
.....abryantKILLspamspam@spam@peaktech.com (work)
adamdbspamKILLspamjuno.com (home)
Parker, CO, USA
Robotics, RC Airplanes, anything using a PIC

On Fri, 5 Mar 1999 18:05:31 -0000 Stuart Meier <.....smeierKILLspamspam.....PAVILION.CO.UK>
writes:
{Quote hidden}

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1999\03\05@152356 by David W. Duley

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In a message dated 3/5/99 11:33:31 AM Pacific Standard Time,
EraseMEsmeierspam_OUTspamTakeThisOuTPAVILION.CO.UK writes:

<< Pin ra4 in a 16F84 application doesn't seem to work as an output in my app
(just turns on a test led)

I have checked...
    Set ra4 as an output in TRISA
    Not set as Tock1 in OPTION bit 5
    Not a faulty chip (programmed another f84 with the same code = same
fault)
    Not the code (worked fine when swapped with ra3 - but still no output on
ra4)

I'm a bit of a newbie, so it may well be something obvious I shouldn't have
overlooked.

Any suggestions, warmly received

Stuart Meier
 >>
Hi Stuart,
RA4 is open drain only.  It can only pull down.  Try Connecting the cathode of
the led (through a 270 ohm resistor) to RA4 and the Anode to the positive
rail.

Dave Duley

1999\03\05@153601 by Vincent Deno

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RA.4 is an open collector output.  You will need to add a pull-up resistor
to "drive" the line.

-Vincent Deno

{Quote hidden}

--------------
Vincent Deno
Design Engineer
Theta Digital Corp.
http://www.thetadigital.com
denovjspamspam_OUTemail.uc.edu
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|_/  /___\  \_|

1999\03\05@200559 by Stuart Meier

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Thanks to all - should have spotted this!

Stuart
-----Original Message-----
From: Peter Schultz <@spam@schupetKILLspamspamDVP.COM>
To: KILLspamPICLISTKILLspamspamMITVMA.MIT.EDU <RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU>
Date: 05 March 1999 20:16
Subject: Re: ra4 on 16F84 inoperable


This a open drain type. It will required pull-up resistor.

Peter Schultz
<spamBeGoneschupetspamBeGonespamdvp.com>
DVP Inc.
3430 Ocean View Blvd. Unit A
Glendale, CA
(818) 541-9020
Fax: (818) 541-9423

>Pin ra4 in a 16F84 application doesn't seem to work as an output in my app

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