If you only want to use RA4 and get a high voltage drive, just tie a
pullup resistor to RA4 from +5 and then connect RA4 to the base of
an NPN transistor rated at 40v or more. Note that a high out from
RA4 will result in a low out from the transistor collector. You
can tie the collector to +40 or whatever via a pullup resistor.

Fr. Tom McGahee

----- Original Message -----
From: Andy Shaw <andy-pl@GLOOMY-PLACE.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Saturday, August 18, 2001 12:05 PM
Subject: [PIC]: RA4 voltage


> Hi Folks,
> A quick question about RA4 when used for output. On most devices it is
open
> collector. What is the max voltage I can pull this up to? For example if I
> wanted to drive a MOSFET from it could I use it to pull down to zero volts
> and have a resistor hooked up to say a 12V supply to turn the FET on? I
have
> a feeling this is not allowed but I thought I would ask. I seem to
remember
> something in the spec for 16F87X products saying 8V or so, but I don't
have
> the spec handy and I can't get to Microchips web site at the moment!
>
> On the same subject what about other common logic families TTL/CMOS etc.
Do
> they have chips that take PIC level logic inputs and have open collector
> outputs that could be used in this way. Or would I be better of using some
> sort of driver chip that is intended for the job?
>
> Sorry if this seems a stupid question, but I really a software kind of
guy!
>
> Andy
>
> --
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>
>

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