GND pins in GPIO connector.
Posted: Wed Aug 22, 2012 1:08 pm
In this post where Eben released the schematics...
http://www.raspberrypi.org/archives/1090
..he said...
"Note: developers of expansion boards should not rely on the connection of expansion connector pins 9, 14, 20 and 25 to GND, pin 4 to 5V or pin 17 to 3V3 and should instead treat these pins as DNC (do not connect). They may be used to expose additional GPIO lines on a subsequent revision of the board."
This would only leave _ONE_ ground connection between the GPIO header and any expansion boards.
I believe the SPI interface can be driven at 10's of MHz, I presume the other GPIO signals can be switched quickly too.
In order to maintain any sort of signal integrity between the RPi and an expansion board you need multiple GND connections. I'd suggest leaving _at least_ pins 6 and 20 as a GND and ideally6, 20 and 25.
If you need more IO extend the connector or add another (spi specific?) but don't knobble the interface speed by trying to rely on _1_ ground.
It would be good to make a decision on this ASAP so expansion board manufacturers know what they can use.
Nial
http://www.raspberrypi.org/archives/1090
..he said...
"Note: developers of expansion boards should not rely on the connection of expansion connector pins 9, 14, 20 and 25 to GND, pin 4 to 5V or pin 17 to 3V3 and should instead treat these pins as DNC (do not connect). They may be used to expose additional GPIO lines on a subsequent revision of the board."
This would only leave _ONE_ ground connection between the GPIO header and any expansion boards.
I believe the SPI interface can be driven at 10's of MHz, I presume the other GPIO signals can be switched quickly too.
In order to maintain any sort of signal integrity between the RPi and an expansion board you need multiple GND connections. I'd suggest leaving _at least_ pins 6 and 20 as a GND and ideally6, 20 and 25.
If you need more IO extend the connector or add another (spi specific?) but don't knobble the interface speed by trying to rely on _1_ ground.
It would be good to make a decision on this ASAP so expansion board manufacturers know what they can use.
Nial