×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Two Vss in a PIC microcontroller?

Two Vss in a PIC microcontroller?

Two Vss in a PIC microcontroller?

(OP)
Hi all,

That could be a stupid question...

In PIC's microcontroller family that have 2 Vss, they are the same point? Vss == to the other Vss?

I mean...
It could help me in the design of the PCB ...
but.. it will let good current flow??

Any one read about it in the datasheet?

well Vss its suposed to be 0v or the GND...

well thanks for your replys!!

bye,
KS

RE: Two Vss in a PIC microcontroller?

its not a good idea to use the two pins as a circuit trace. I measured 7 ohms between the pins on a 16f870 so they must go to seperate pads on the die.

RE: Two Vss in a PIC microcontroller?

Using the chip internal trace as a means of cheating on the PCB is an extremely bad idea, particularly for some like a PIC, since the current rating is probably pretty low.  

>>  You might simply blow the trace altogether
>>  You might thoroughly degrade the reliability of the PIC, by running too much current in the chip trace, which may cause electromigration failure on the device.
>>  You may seriously degrade the noise margin of the device, since one end of the chip will wind up at a higher potential than the other.

TTFN

RE: Two Vss in a PIC microcontroller?

Oddly enough, they put two ground pins (Vss pins) on devices so that you can ground both of them to a nice solid copper ground.

Some devices have many ground pins (10 or more) and they should all be connected to the same copper ground trace or plane.

It reduces noise pickup.

You don't have to try very hard to turn on substrate diodes which can cause all sorts of problems. Mostly nasty one.

RE: Two Vss in a PIC microcontroller?

Both should be connected to ground.

RE: Two Vss in a PIC microcontroller?

The same can been true for many chip pins marked NC.
In this case the NC doesn't always mean that the pin is NOT CONNECTED it often means DO NOT CONNECT!!!
So check before using a NC pin as a convenient route for a PCB trace.
I once spent many hours debugging a circuit which had worked fine in breadboard form but failed totally on the PCB.

Electricliff

RE: Two Vss in a PIC microcontroller?

I heared that numerous Grounds and/ or NC are sometimes for heast-sink purpose from the junction. It sounds and will do this job, but I'm not quit sure if they are there to do so.


Cheers


You can live in your car, but you can't drive your House!

RE: Two Vss in a PIC microcontroller?

The reason there are two GNDs (VSubStrate)on the PIC is because Pics have much higher pin source and sinking than the typical micro, 25mA a pin, 200mA a Port.  The very tiny wire that connects the leads to the IC and the IC structure need multiple pins to support this current.  The same reason a Pentium 4 has 181, you read that right, one hundred eighty one ground pins, never mind the 85 VCC pins.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources