Browsing the datasheets, I notice some 
varieties of PICs have multiple Vss and/or 
Vdd pins; must they *all* be connected to 
power, or are they redundant to provide 
PCB routing flexibility?

I'm referring to straight Vss/Vdd, as 
opposed to special stuff like Avss/Avdd. 

No, I'm not planning to power a whole section 
of circuits via my micro, but I am wondering 
what the intent is for those pins.

TIA

Randy Day wrote:
> Browsing the datasheets, I notice some 
> varieties of PICs have multiple Vss and/or 
> Vdd pins; must they *all* be connected to 
> power, or are they redundant to provide 
> PCB routing flexibility?
> 
> I'm referring to straight Vss/Vdd, as 
> opposed to special stuff like Avss/Avdd. 
> 
> No, I'm not planning to power a whole section 
> of circuits via my micro, but I am wondering 
> what the intent is for those pins.

Not only should they all be connected, you should add bypass 
capacitors between all close pairs of Vss Vdd pins.  Chips 
with lots of possible outputs can pull large currents 
through the Vss and Vdd pins, so having more than 1 pair 
reduces the IR and inductive drop of the pins and wire 
bonds.  This is especially important if you plan on using 
any of the chip analog functions without having supply 
voltage change errors and noise added into their function.

"Randy Day" <r...@shaw.cax> wrote in message
news:4...@shaw.cax...
> Browsing the datasheets, I notice some
> varieties of PICs have multiple Vss and/or
> Vdd pins; must they *all* be connected to
> power, or are they redundant to provide
> PCB routing flexibility?
>
> I'm referring to straight Vss/Vdd, as
> opposed to special stuff like Avss/Avdd.
>
> No, I'm not planning to power a whole section
> of circuits via my micro, but I am wondering
> what the intent is for those pins.
>
> TIA

Well, I've just pulled off a Vss on a PIC 16F873 on the protoboard and it
carried on working.
I wouldn't intentionally leave 'em off though, as they'll be needed to
maintain good noise margins under poor working conditions.

Randy Day wrote:
> Browsing the datasheets, I notice some 
> varieties of PICs have multiple Vss and/or 
> Vdd pins; must they *all* be connected to 
> power, or are they redundant to provide 
> PCB routing flexibility?
> 
> I'm referring to straight Vss/Vdd, as 
> opposed to special stuff like Avss/Avdd. 
> 
> No, I'm not planning to power a whole section 
> of circuits via my micro, but I am wondering 
> what the intent is for those pins.
> 
> TIA
I don't know which Pic you're looking at how ever, If it's
anything like other chips that do that. If you look at the
Vdd description. It maybe labeled as Vdd 2 or something in that
order.
   To give you an example of why this would be..
  Lets assume the PIC's internal logic is only 5 volts and you
have a bunch of outputs.
   Now, if you decided to operate these outputs in SOURCE mode,
you could then select a different output voltage other than the
one the CPU area is using..
    for example, the output SOURCE voltage could be 12 volts..

  The other options are, internally isolated outputs. this would
require a different Vdd and Vss to make it truly isolated output or,
  if you decide that you don't need the isolation, you then tied them
to the same rail.

   Also, they some times offer multiple Rail lines for construction and
  internal power stability..


-- 
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

Jamie wrote:

> Randy Day wrote:
> > Browsing the datasheets, I notice some
> > varieties of PICs have multiple Vss and/or
> > Vdd pins; must they *all* be connected to
> > power, or are they redundant to provide
> > PCB routing flexibility?
> >
> > I'm referring to straight Vss/Vdd, as
> > opposed to special stuff like Avss/Avdd.
> >
> > No, I'm not planning to power a whole section
> > of circuits via my micro, but I am wondering
> > what the intent is for those pins.
>
> I don't know which Pic you're looking at how ever, If it's
> anything like other chips that do that. If you look at the
> Vdd description. It maybe labeled as Vdd 2 or something in that
> order.
>    To give you an example of why this would be..
>   Lets assume the PIC's internal logic is only 5 volts and you
> have a bunch of outputs.
>    Now, if you decided to operate these outputs in SOURCE mode,
> you could then select a different output voltage other than the
> one the CPU area is using..
>     for example, the output SOURCE voltage could be 12 volts..
>
>   The other options are, internally isolated outputs. this would
> require a different Vdd and Vss to make it truly isolated output or,
>   if you decide that you don't need the isolation, you then tied them
> to the same rail.
>
>    Also, they some times offer multiple Rail lines for construction and
>   internal power stability..

More random STUPIDITY from the Janie TROLL.

Graham

Eeyore wrote:

> 
> Jamie wrote:
> 
> 
>>Randy Day wrote:
>>
>>>Browsing the datasheets, I notice some
>>>varieties of PICs have multiple Vss and/or
>>>Vdd pins; must they *all* be connected to
>>>power, or are they redundant to provide
>>>PCB routing flexibility?
>>>
>>>I'm referring to straight Vss/Vdd, as
>>>opposed to special stuff like Avss/Avdd.
>>>
>>>No, I'm not planning to power a whole section
>>>of circuits via my micro, but I am wondering
>>>what the intent is for those pins.
>>
>>I don't know which Pic you're looking at how ever, If it's
>>anything like other chips that do that. If you look at the
>>Vdd description. It maybe labeled as Vdd 2 or something in that
>>order.
>>   To give you an example of why this would be..
>>  Lets assume the PIC's internal logic is only 5 volts and you
>>have a bunch of outputs.
>>   Now, if you decided to operate these outputs in SOURCE mode,
>>you could then select a different output voltage other than the
>>one the CPU area is using..
>>    for example, the output SOURCE voltage could be 12 volts..
>>
>>  The other options are, internally isolated outputs. this would
>>require a different Vdd and Vss to make it truly isolated output or,
>>  if you decide that you don't need the isolation, you then tied them
>>to the same rail.
>>
>>   Also, they some times offer multiple Rail lines for construction and
>>  internal power stability..
> 
> 
> More random STUPIDITY from the Janie TROLL.
> 
> Graham
> 


  Come back for more "Arm chair bull shit artist" antics

   Your comments display lack of colour with your responses
which is parallel to your intelligence.

    Ever hear the terms?

   "You were nothing but a little squirt"

  or,

   "I scraped you off the sheets" ?

  something you might have heard when you were a kid?

   So go take a hike pecker head.

-- 
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

Eeyore wrote:
> Jamie wrote:
>
>> Randy Day wrote:
>>> Browsing the datasheets, I notice some
>>> varieties of PICs have multiple Vss and/or
>>> Vdd pins; must they *all* be connected to
>>> power, or are they redundant to provide
>>> PCB routing flexibility?
>>>
>>> I'm referring to straight Vss/Vdd, as
>>> opposed to special stuff like Avss/Avdd.
>>>
>>> No, I'm not planning to power a whole section
>>> of circuits via my micro, but I am wondering
>>> what the intent is for those pins.
>>
>> I don't know which Pic you're looking at how ever, If it's
>> anything like other chips that do that. If you look at the
>> Vdd description. It maybe labeled as Vdd 2 or something in that
>> order.
>>    To give you an example of why this would be..
>>   Lets assume the PIC's internal logic is only 5 volts and you
>> have a bunch of outputs.
>>    Now, if you decided to operate these outputs in SOURCE mode,
>> you could then select a different output voltage other than the
>> one the CPU area is using..
>>     for example, the output SOURCE voltage could be 12 volts..
>>
>>   The other options are, internally isolated outputs. this would
>> require a different Vdd and Vss to make it truly isolated output or,
>>   if you decide that you don't need the isolation, you then tied them
>> to the same rail.
>>
>>    Also, they some times offer multiple Rail lines for construction
>>   and internal power stability..
>
> More random STUPIDITY from the Janie TROLL.
>
> Graham

At least he's trying to be helpful.  OTOH, you're just being a 
dick........AGAIN!

Now to get nearer to the topic at hand, we're all still waiting to see some 
modest demonstration of your expert coding ability.  I"ve been playing with 
one of these for a couple of weeks in my spare time, using some icky old C, 
it's pretty neat IMO:
http://www.sparkfun.com/commerce/product_info.php?products_id=8280
Get one and we'll have a contest to see who can come up with the neatest 
application using just the onboard hardware. 

Anthony Fremont wrote:

> Eeyore wrote:
> >
> > More random STUPIDITY from the Janie TROLL.
>
> At least he's trying to be helpful.  OTOH, you're just being a
> dick........AGAIN!

The problem with Janie is that she gives VERY BAD 'advice'. For her she sees it
as a competition to be the stupidest poster in the thread and usually wins the
stupidest award by far.

Graham

Eeyore wrote:

> 
> Anthony Fremont wrote:
> 
> 
>>Eeyore wrote:
>>
>>>More random STUPIDITY from the Janie TROLL.
>>
>>At least he's trying to be helpful.  OTOH, you're just being a
>>dick........AGAIN!
> 
> 
> The problem with Janie is that she gives VERY BAD 'advice'. For her she sees it
> as a competition to be the stupidest poster in the thread and usually wins the
> stupidest award by far.
> 
> Graham
> 
She? Should I drop my trousers and stick what I have hanging there some 
where for you? Or should I just wave it around in front of you since you 
obviously don't have one.

    Typical ignorant social disordered psychopath.

  P.S.
    In case you wasn't aware, we're out of the dark ages. It is no longer
a standard practice to test voltage with wet fingers. I just thought
I would remind you of that because you seem to be a few cells short of a
picnic.



-- 
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

"Jamie" <j...@charter.net> wrote in message 
news:HFvYi.161$5...@newsfe02.lga...
> Eeyore wrote:
>
>>
>> Anthony Fremont wrote:
>>
>>
>>>Eeyore wrote:
>>>
>>>>More random STUPIDITY from the Janie TROLL.
>>>
>>>At least he's trying to be helpful.  OTOH, you're just being a
>>>dick........AGAIN!
>>
>>
>> The problem with Janie is that she gives VERY BAD 'advice'. For her she 
>> sees it
>> as a competition to be the stupidest poster in the thread and usually 
>> wins the
>> stupidest award by far.
>>
>> Graham
>>
> She? Should I drop my trousers and stick what I have hanging there some 
> where for you? Or should I just wave it around in front of you since you 
> obviously don't have one.
>
>    Typical ignorant social disordered psychopath.
>
>  P.S.
>    In case you wasn't aware, we're out of the dark ages. It is no longer
> a standard practice to test voltage with wet fingers. I just thought
> I would remind you of that because you seem to be a few cells short of a
> picnic.

Why discourage him from voltage testing with a wet finger?!