greiginsydney
Posts: 8
Joined: Tue Sep 25, 2018 9:17 pm

Pi Zero W has no pullups on I2C pins, but the Zero does?

Sat Oct 06, 2018 8:38 am

Hi,

I notice there's a difference in the published 'reduced' circuits for the Zero and the Zero W.

https://www.raspberrypi.org/documentati ... /README.md

The Zero shows as having pullups on the SDA & SCL lines, which are not present in the "W" version.

Image

Can anyone confirm if that's an oversight in the circuit or correct?

Thanks,


Greig.

PhilE
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 4511
Joined: Mon Sep 29, 2014 1:07 pm
Location: Cambridge

Re: Pi Zero W has no pullups on I2C pins, but the Zero does?

Mon Oct 08, 2018 2:01 pm

The handling of GPIO2 and GPIO3 is the same (and correct) on both devices. The two extracts you post are from opposite ends of the GPIO2 trace. The Zero 1.3 schematic includes both ends, whereas the Zero W 1.1 schematic omits the BCM2835 end, which is where the pull-ups are.

greiginsydney
Posts: 8
Joined: Tue Sep 25, 2018 9:17 pm

Re: Pi Zero W has no pullups on I2C pins, but the Zero does?

Mon Oct 08, 2018 8:37 pm

Thanks Phil.

As these are the only circuits available for the Zero (and are abridged anyway) can I ask that the W’s be updated to show the resistors?

Without knowing they’re there, someone adding their own pair is going to result in a pretty strong pull-up on the bus, or might otherwise be experiencing strange behaviour if they use the pins for IO in the belief they DONT have pull-ups.


- G.

User avatar
Burngate
Posts: 6526
Joined: Thu Sep 29, 2011 4:34 pm
Location: Berkshire UK Tralfamadore

Re: Pi Zero W has no pullups on I2C pins, but the Zero does?

Tue Oct 09, 2018 8:48 am

Given that the GPIO pads can handle up to 16mA, even with 1k8 pull-ups already there, you could add your own pull-ups down to 240Ω without breaking anything.
Assuming a maximum of 8mA, that rises to 510Ω

While it would be nice to have full schematics of all the Pi range, we're unlikely to get them - it's been discussed at length else-where on this forum.

hippy
Posts: 11966
Joined: Fri Sep 09, 2011 10:34 pm
Location: UK

Re: Pi Zero W has no pullups on I2C pins, but the Zero does?

Tue Oct 09, 2018 10:20 am

I am not sure why the reduced Zero W schematic doesn't show the exact same as the original reduced Zero schematic, adjusted as appropriate where there are changes of course.

If "it's not there for the W but can be determined by reference to the original" it doesn't protect IP or anything; it just makes it more difficult to find the information, costs time and effort to give an answer. The removal of things even suggests something has changed, that how it is on the Zero W is different to the original.

That just leads to questions like this one which no one can answer with any certainty other than those with access to the full schematics or those who undertake some degree of reverse engineering.

greiginsydney
Posts: 8
Joined: Tue Sep 25, 2018 9:17 pm

Re: Pi Zero W has no pullups on I2C pins, but the Zero does?

Wed Oct 10, 2018 6:18 am

Thanks @hippy, glad I'm not alone in that reasoning.

- G.

User avatar
HermannSW
Posts: 5184
Joined: Fri Jul 22, 2016 9:09 pm
Location: Eberbach, Germany

Re: Pi Zero W has no pullups on I2C pins, but the Zero does?

Wed Oct 10, 2018 12:17 pm

I agree that as it is, it is wrong.

It seems that Pi ZeroW BCM2835 schematics only displays connections "different" to BCM2835 connections of Pi Zero:
Image

If that is correct, then changing "BCM2835" to "BCM2835 (additions to Pi Zero shown only)" or similar would fix the issue.

These are the steps to get it fixed: I did documentation correction pull request myself some time ago, and now its part of official documentation, so the process really works:
https://www.raspberrypi.org/forums/view ... 9#p1336355
https://hermann-sw.github.io/planar_graph_playground
https://stamm-wilbrandt.de/en#raspcatbt
https://github.com/Hermann-SW/memrun
https://github.com/Hermann-SW/Raspberry_v1_camera_global_external_shutter
https://stamm-wilbrandt.de/en/Raspberry_camera.html

hippy
Posts: 11966
Joined: Fri Sep 09, 2011 10:34 pm
Location: UK

Re: Pi Zero W has no pullups on I2C pins, but the Zero does?

Wed Oct 10, 2018 2:19 pm

HermannSW wrote:
Wed Oct 10, 2018 12:17 pm
While making third-party changes is perfectly easy for text-based documentation it's not so easy when it's a PDF which has copyright upon it.

I'm also not clear how any third-party can be adding something missing into a schematic when they don't know exactly what is missing and won't know if what they are adding is actually correct.

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 31007
Joined: Sat Jul 30, 2011 7:41 pm

Re: Pi Zero W has no pullups on I2C pins, but the Zero does?

Wed Oct 10, 2018 3:11 pm

Passed this on to the HW team, they are discussing the best course of action. No idea how long it will be, they are a tad busy.
Principal Software Engineer at Raspberry Pi Ltd.
Working in the Applications Team.

greiginsydney
Posts: 8
Joined: Tue Sep 25, 2018 9:17 pm

Re: Pi Zero W has no pullups on I2C pins, but the Zero does?

Wed Oct 10, 2018 8:05 pm

Thanks @Jamesh, much appreciated.

- G.

User avatar
HermannSW
Posts: 5184
Joined: Fri Jul 22, 2016 9:09 pm
Location: Eberbach, Germany

Re: Pi Zero W has no pullups on I2C pins, but the Zero does?

Thu Oct 11, 2018 1:16 pm

hippy wrote:
Wed Oct 10, 2018 2:19 pm
While making third-party changes is perfectly easy for text-based documentation it's not so easy when it's a PDF
You can easily change by "pdf2ps" and then edit with eg. "vi". Of course that gives a .ps where a .pdf is needed.
which has copyright upon it.
No problem, please look at Raspberrypi documentation license:
https://github.com/raspberrypi/document ... LICENCE.md
is"Creative Commons Attribution 4.0 International Licence":
https://creativecommons.org/licenses/by-sa/4.0/

Code: Select all

You are free to:
Share — copy and redistribute the material in any medium or format
Adapt — remix, transform, and build upon the material
for any purpose, even commercially.
 This license is acceptable for Free Cultural Works.
The licensor cannot revoke these freedoms as long as you follow the license terms.
I'm also not clear how any third-party can be adding something missing into a schematic when they don't know exactly what is missing and won't know if what they are adding is actually correct.
That is what a pull request is for, the Raspberrypi people will review, change if needed, accept if they want.

Raspberrpypi is interested in getting pull requests for documentation.
So if anybody has software to edit PDFs he can do and do a pull request as I stated,

A pull request will take less time for the busy Raspberrypi people than to do the changes completely on their own.
https://hermann-sw.github.io/planar_graph_playground
https://stamm-wilbrandt.de/en#raspcatbt
https://github.com/Hermann-SW/memrun
https://github.com/Hermann-SW/Raspberry_v1_camera_global_external_shutter
https://stamm-wilbrandt.de/en/Raspberry_camera.html

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 31007
Joined: Sat Jul 30, 2011 7:41 pm

Re: Pi Zero W has no pullups on I2C pins, but the Zero does?

Mon Feb 04, 2019 9:02 am

I just uploaded a new schematic to github, so should be live on the website soon.
Principal Software Engineer at Raspberry Pi Ltd.
Working in the Applications Team.


Return to “General discussion”