why two ground pins?

[Rohitchampion]

If you see 8086 microprocessor pin diagram, there are two GROUND pins, PIN1 and PIN20.
Can anybody explain why two ground pins are used on 8086?

I searched on google but all are giving different answers so I am posting here.

 

[JimB]

If you look at the PIC 16F887, you will see that that has two ground and two supply pins.

I can think of two possible reasons:

Two connections makes for a lower impedance connection.

One connection for each of two different parts of the chip, makes life easier for the guy designing the silicon.

JimB

 

[KeepItSimpleStupid]

I can think of better reasons for the PIC:
Analog ground, digital ground
The pin for the ratiometric reference ground.

 

[NorthGuy]

One connection for each of two different parts of the chip, makes life easier for the guy designing the silicon.

And then datasheet suggests that all ground pins have to be connected, which, if followed, makes PCB design harder. How come the guy designing the silicon is more important than the PCB guy?

 

[KeepItSimpleStupid]

Because in silicon, its harder. No layers. Wire bonds to anywhere on the chip. No insulated wire though.

I did some manual ultrasonic gold wire bonds before.

 

[JimB]

I can think of better reasons for the PIC:
Analog ground, digital ground
The pin for the ratiometric reference ground.

A reasonable supposition, however, the PIC datasheet makes no mention (as far as I can see) of separate analogue and digital grounds.

Northguy said:

How come the guy designing the silicon is more important than the PCB guy?

I did not intend to imply that anyone was more important than anyone else.
Maybe it is a good idea to provide supplies to both sides of the chip, rather than having the supplies for one side flow through the other side.

I don't know, just supposition* on my part.

JimB


* Supposition = A guess that has been to university.

 

[tronitech]

I think you're right JimB. It's probably down to distributing clean power "across" the chip. Look at something like the i7 900 series processors, there are in the region of 200 of each supply and ground pins.

 

[atferrari]

* Supposition = A guess that has been to university.

An educated guess in short?

 

[Rohitchampion]

Thanks JimB
And yeah there are no separate analog and digital grounds.

 

[atferrari]

I think you're right JimB. It's probably down to distributing clean power "across" the chip. Look at something like the i7 900 series processors, there are in the region of 200 of each supply and ground pins.

I stopped counting at 220. WOW!

 

[large_ghostman]

some pics have analogue and digital supplies! I forget the naming convention but for example the ADC's on some pics have there own supply pin's, even if you use the internal ref etc you still have to power the ADC pins

 

[rc3po]

If you look at the PIC 16F887, you will see that that has two ground and two supply pins.

I can think of two possible reasons:

Two connections makes for a lower impedance connection.

One connection for each of two different parts of the chip, makes life easier for the guy designing the silicon.

JimB

Thanks JimB. I'm new to uControllers and I just assumed that the multiple Power & Ground pins were to allow the Chips to carry more current. So I guess I was wrong.

 

[large_ghostman]

Thanks JimB. I'm new to uControllers and I just assumed that the multiple Power & Ground pins were to allow the Chips to carry more current. So I guess I was wrong.

In some ways your right, if the pic had to internally connect from one side to the other, then surely the current available would drop? Not too sure now Ive said it! to me what goes on inside is the pics business unless it smokes! . The bit that annoys me though is they tend to cross the VDD and GND pins on each side! they never seem to be opposite.

 

[JimB]

The bit that annoys me though is they tend to cross the VDD and GND pins on each side! they never seem to be opposite.

Just to keep you on your toes!
Prevents complacency.

JimB

 

[rc3po]

In some ways your right, if the pic had to internally connect from one side to the other, then surely the current available would drop? Not too sure now Ive said it! to me what goes on inside is the pics business unless it smokes! . The bit that annoys me though is they tend to cross the VDD and GND pins on each side! they never seem to be opposite.

I'm still reading books and learning how to use my new Arduino so I haven't looked into the Chips internal structure.
Having more Pow/ Grd pins may also help keep the Chip cooler instead of trying to send all of the current through 2 pins. I usually get yelled at around here for using common sense. Perhaps I'm a glutton for punishment?