VSS and VDD?

[Sam_40]

Hello,
It's an off top question, I apologize for that.
Some PICs have multiple pins for power namely VSS and VDD.
Reading a lot of AN by MC and TI and other topics, one will understand as its not a good idea to connect these pins and only use one and have a bypass cap between VSS and VDD (I mean connect all the VSS together and VDD together) close to the uC.

I do believe connect all VSS's together and all VDD's may create loop that will generate an unwanted noise and may affect the usefulness of the ground plane.

If that was the case why the manufacturer provide multiple pins?

What do you guys suggest?

Thank you,

[temtronic]

I've always thought it was a waste of 2 pins used for power. Old school micros like the Z80 ran fine on one pair. Have to admit I connect them both and after 10-15 years have never had 'ground loop' or 'noise' issues. I also use the dreaded 'white breadboards' for quick bench testing as well as wirewrap and solder stitching. If it works using them, it'll work better on a real PCB.
As for why multiple pins, it may be that since the die is so small, they need more 'wire' to get the electrons in and out, especially at high speeds. You'd have to talk to someone who actually designs the silicon though. Me, I just use and abuse PICs !

[Sam_40]

I always connected all the VSS together and VDD together too, Always when design my PCB or when soldering the component to BusBoard Prototype board, I make sure the uC is terminal connection and I don't use the VSS or VDD terminals as pass through connection to other components.
Most datasheet shows VSS and VDD can handle more than 200mA.
I was just making sure and was wondering how is my expert friends at this forum do it.
Thank you

[Ttelmah]

The 'point' about these is that on larger dies, the resistance of the internal tracking between parts of the chip becomes significant. Hence you need to have all of them fed, or you may find sub-sections of the chip stop working right with voltage differences between the sections.
They need to each be fed just like any other power pin. Ideally just connect to a power/ground plane, with decoupling close to the pin.
Even quite a basic PIC has a larger die than the z-80. Much more RAM, and of course the ROM which the z-80 has externally rather than in the chip. Then add the peripherals as well. The actual 'processor' die of a z-80 is larger than a PIC16, but the other stuff makes the overall number of gates larger.

[rnielsen]

I've worked at semi-conductor companies for over 27 years now and know that it's best to connect all of the GND pins together and VDD pins together. The VDD/GND pins don't always connect together internally. If they do, there can be a trace run that will cause a voltage drop to internal circuits if you don't connect all of the pins.

Ronald

[Sam_40]

Thank you guys for the inputs, I will continue connecting the VSS together and the power pins together.