40 Pin PIC's - Wiring question

[gramo]

Just trying to find some solid evidence if both sets of Vdd and Vss are actually required to be connected on 40 Pin PIC's

I've tried only connecting one side in a couple of different applications without any issues for stability..


Your thoughts/links?

 

[futz]

Here's a previous thread on the subject:

 

[picbits]

déja vu

As above - was discussed a few days ago

 

[gramo]

Thanks guys, but it appears to be all 'hear-say', is there any hard evidence on the matter?

I guess if there was, it would have come up in that

 

[mneary]

Just trying to find some solid evidence if both sets of Vdd and Vss are actually required to be connected on 40 Pin PIC's

Define "required".

What are your criteria? Reliability? I/O driving capability? Error free operation? Electromagnetic emissions? Noise immunity?

 

[gramo]

One factor does come to mind - but it is derived just from common sense;

Perhaps the dual power pins accommodate the possibility of all ports being driven as outputs.​

I'd really like to see some official notes on the matter though

 

[futz]

One factor does come to mind - but it is derived just from common sense;

Perhaps the dual power pins accommodate the possibility of all ports being driven as outputs.​

I tend to think the opposite (just my opinion). I think they put pins on both sides just to make board design easier. Use whichever pins work best with your design. Gives you the option to find the easiest way in when routing. I'm probably wrong. I know lots of people disagree with me.

Of course I hook em both up anyway, just in case.

I'd really like to see some official notes on the matter though

YES.

 

[gramo]

Ticket has been posted with microchip - I'll let you know how it goes

 

[mneary]

Maybe you could measure the resistance and reactance between the two sets of pins.

 

[gramo]

Response from Microchip

My question for Microchip;

I have had a number of inquiries and am interested myself to know the full extent of the requirements for connecting both sets Vdd and Vss on any 40 Pin PIC Micro. Are there situations where they are not required? Is there extended information regarding the matter?

Practical experimenting suggests that only one set of Vdd and Vss are required.

Their response;

If device is having multiple power pins, then it will be advisable to tie the together. This
Is on of the good practice which needs to be followed in hardware application circuit design.
Refer the presentation of "power considerations" topic in the following web link:
https://www.electro-tech-online.com/custompdfs/2007/12/power.pdf

 

[gramo]

So I guess the end answer is yes - You must connect both Vdd and Vss pins

 

[kchriste]

That link should be in the locked sticky PIC FAQ by Jay.slovak:
https://www.electro-tech-online.com/threads/pic-newcomers-please-read-upd-0xd1.15035/
Lots of good PIC info in a large font for noobs!