> On Thu, May 01, 2003 at 09:04:12PM -0600, Dwayne Reid wrote:
> > At 01:13 AM 4/30/03 -0700, Ben Jackson wrote:
> >
> > >On the 16F628 (my actual target in this case) the open drain output
> > >RA4 has protection to VDD as well, while RA5 (the input-only pin which
> > >is multiplexed with MCLR) does not.  Of course, being input-only it's
> > >not going to work for this circuit.
> >
> > That part of the data sheet is wrong.  Please look at DS40300C - page
> 127
> >
> > "Voltage on MCLR and RA4 with respect to V SS  -0.3 to +14V"
>
> -----Original Message-----
> From: Ben Jackson [SMTP:ben@BEN.COM]
> Sent: Friday, May 02, 2003 4:52 AM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: how to detect "ON" button in this auto-off circuit
>
> Thanks for the tip!  I tried it out and you are correct (weak voltage
> on RA4 and RA5 while the chip is off does not show up on VDD, but on
> the other PORTA and PORTB lines it does).
>
> I'll double check the electrical characteristics section next time.
>
Note that 14v is specified as the "Absolute Maximum", a parameter you should
NEVER design against.  Read the small print underneath, this is the voltage
that the PIC can survive without breaking and correct operation is not
implied or guaranteed under these conditions.  Look further on in the
electrical specs and you will see the maximum voltage for RA4 is 8.5 volts
(Parameter D150).

Regards

Mike


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