Two Vss in a PIC microcontroller?

[KammutierSpule]

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

 

[cbarn24050]

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.

 

[IRstuff]

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

 

[zeitghost]

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.

 

[buzzp]

Both should be connected to ground.

 

[Electricliff]

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

 

[zimbali]

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!

 

[60hzhmmm]

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.