PICs and Vss/Vdd

[Randy Day]

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

 

[John Popelish]

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.

 

[john jardine]

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.

 

[Jamie]

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..

 

[Eeyore]

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

 

[Jamie]

Jamie wrote:




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.

 

[Anthony Fremont]

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.

 

[Eeyore]

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

 

[Jamie]

Anthony Fremont wrote:




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.

 

[ian field]

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?!

 

[Anthony Fremont]

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

How are your PIC adventures going?

 

[ian field]

How are your PIC adventures going?

Still trawling through back issues of EPE, that's what I have the most
downloaded sample code for. One problem is that the TK3 and SEND programmes
have an odd convention with the ORG instruction, using ORG 4 & ORG 5 rather
than ORG 0, this could be an unwanted hassle as EPE has standardised on LPT
port programmers and my Velleman is RS232 port.

The PIC in Practice book is a bit vague on configuration and header file,
I've jumped to chapter 6 which is supposed to explain this as I don't see
much point in trying to understand the code examples while I haven't a clue
how to set up the configuration that obviously has to come first.