Raspberry Pi 3 Model B GPIO 40 Pin Block Pinout

Hi Graham,

Apparently it is compatible electrically with the Pi 2. However we know that I/O pads can be different. And we know schematics and detailed electrical specifications are important.

Basically you're preaching to the converted : ) Many people feel your pain, as I do. The source to direct this to is the Raspberry Pi Foundation, but they haven't listened to this issue in about 4 years.. if you ask them, you'll maybe get a response from them saying "you have all the information that is needed, schematics have no benefit over what information is already available". However we as engineers know this is not the case. You could ask Broadcom for a copy of the BCM.. datasheet. Again, I doubt this will get you far, just letting you know that others have asked for years on the RPF forum which has Broadcom and ex-Broadcom engineers frequenting it.

And for what it's worth, the reason for wanting an actual data sheet is to avoid incorrect info like here:

http://www.scribd.com/doc/101830961/GPIO-Pads-Control2

.. in which someone managed to get hold of a BCM2835 datasheet that's more complete than the one from RasPi site (yay for that, but I wish I could find the same doc), and actually includes a few details about controlling I/O drive current. (This is absolutely essential info, and even the info in this excerpt isn't enough to determine whether all GPIOs are controlled together, which seems silly, or individually or in groups of what size? )

And then this user incorrectly interprets VIL and VIH specs as pertaining to outputs.

(And BTW, interestingly if those VIL/VIH values are to be believed, the inputs appear to use 3.3V-scaled version of old-style TTL compatible levels, rather than CMOS 1/3*VDD and 2/3*VDD levels. Essential to know if interfacing to, you know, other devices.)

And of course that all doesn't necessarily pertain to RasPi3.

Having to guess electrical specs is pure amateur hour. Surely these chips and boards were actually engineered, and there are some proper docs somewhere?

Graham

Thanks to @shabaz and @clem57 for your comments. (That mosiac doc site is nice!)  But...

I want to point out that I'm asking specifically about Raspberry Pi THREE. I realize that RasPi 3 may have been designed to be compatible with 2 and previous, hence experience with previous models may be illuminating.

However, to be confident rather than guessing, what I want to know is actual official info on:

(a)  whether the RPi3's I/O logic voltage standard is actually 3.3V.

(b) whether the header I/O pins are directly connected to the SoC (hence SoC datasheet electrical specs pertain, though I'm not seeing a datasheet on the BCM2837 anywhere), or via buffers, in which case what sort of buffers?

No schematic means users are helpless to determine trivial things like this for themselves.

Again, thanks for responses here, just hoping someone is able to point to official word on these basic questions.

Graham

Just for you gwideman

This is an equivalent answer (no warranty here)

The Raspberry Pi's GPIO pins are quite versatile, and you can modify many of their characteristics from software. You can turn on/off input pin hysteresis, limit output slew rate, and control source and sink current drive capability from 2 mA to 16 mA in 2 mA increments. These properties are set for the GPIO block as a whole, not on a pin-by-pin basis.

Source/sink current capability does not limit the current into or out of the pin, but only specifies the maximum current for which the output signal high/low voltage specifications will be met. If misused, output pins can be damaged by excessive current irrespective of the source/sink current programmed. After a reset, the RPi comes up with the GPIO outputs set to 8 mA drive capability.

Source: GPIO Electrical Specifications, Raspberry Pi Input and Output Pin Voltage and Current Capability

Please mark helpful if this helps,

Clem

Hi Graham,

The Raspberry Pi doesn't have such detailed information regarding the circuit, and there are no full schematics available - it is kind of (in)famous for this for many years now.

The closest to official information is at these locations:

https://www.raspberrypi.org/documentation/hardware/raspberrypi/README.md

(Click on the GPIO link there - the information there is not much however) and

https://www.raspberrypi.org/forums/viewtopic.php?f=44&t=12248

and

https://www.raspberrypi.org/forums/viewtopic.php?f=63&t=25335

(Notice the RPF forum moderators there have confirmed that to be about as much as you'll get).

Given the absence of such information (you can ask at raspberrypi.org as much as you like, they won't supply additional documentation), here are the practical answers to your questions, from experience:

(a). 3.3V LVTTL logic levels, don't exceed 3.3V

(b) Nope, not 5V tolerant because any documentation does not state it. Some people believe there is some tolerance from experiments, but I wouldn't do that

(c) See the link earlier. A few mA, or higher but depends how many you simultaneously drive.

(d) In general don't connect to a source (unless through a reasonably high impedance) until the RPI is powered up.

If you are looking for practical input and output circuits that you can use for interfacing to the 'pi (and some examples for 5V circuit interfacing to the pi), see here:

Raspberry Pi GPIO Explained