On Tue, Oct 23, 2001 at 10:00:37AM +0100, Kevin Blain wrote:
> which is which?

It's not as cut and dried as analog/digital. The bottom line is that a chip
is laid out in 3 dimensional space. As real estate fills up it becomes more
difficult to route power and ground to some areas of the chip. Hence the
multiple power pins.

This is a non-problem that one should not overthink. Always connect all power
pins unless the data sheet gives specific guidelines as to why all power pins
should not be connected.

BAJ
>
> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Vasile Surducan
> Sent: 23 October 2001 07:31
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [PIC]: 16F877 - Why two sets of power pins?
>
>
> analogic and digital section.
> Vasile
>
> On Tue, 23 Oct 2001, Bala Chandar wrote:
>
> > While using the 16F877, I have been connecting only one set of power
> supply
> > pins (+5V and Gnd to pins 32 & 31) and haven't faced any problems so far.
> >
> > Sometime back, someone in this list had asked why there are two Vdd and
> two
> > ground pins in 16F877. I was under the impression that it is there merely
> to
> > ensure pinout compatibility with 28 pin devices, so that the socket in the
> > programmer is suitable for both.
> >
> > But when I checked with the multimeter, I was surprised to find a
> resistance
> > of around 2.5 ohms between the two Vdd pins (11 & 32) and the two ground
> > pins (12 & 31). If the two pins are internally connected, should not the
> > resistance be zero ohm? Or is it necessary to tie both the pins together
> for
> > some reason?
> >
> > Any comments?
> >
> > Regards,
> > Bala
> >
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> >
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