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Improper SPI levels on WIFI-Shield

Posted: Fri Mar 13, 2020 4:33 am
by shen
Hi everyone,
I'd like to tell you about a phenomenon i had in my device and how it should be solved.
I just found that the SPI lines are not well-defined even if i work with the official exmples.
what i found out is that the SPI default level which supposed to be 0V (except for NSS) is somewhere between 0.9-1.1v which means that it might work.
what i also found out is that in the ATWINC1500 data sheet they say that it has internal pull-ups by default on all GPIOs.
in order to remove it, one should send a proper command, i did that in my code (i work bare-metal) and now i see proper digital levels 0v,3.3v.
just to make clear: these pull-ups cause a constant 33uA current consumption per GPIO which for some applications is critical.
yours,
Shen

Re: Improper SPI levels on WIFI-Shield

Posted: Fri Mar 13, 2020 7:04 am
by iabdalkader
The internal pull-ups should be left enabled so SPI pins are not floating when the cam is in reset or low-power, or before SPI is initialized.

Re: Improper SPI levels on WIFI-Shield

Posted: Sat Mar 14, 2020 2:55 am
by shen
That´s correct, but even when the module is initialized and transmitting frames the pull-ups are still high.
my point is, maybe in the initialization process a ¨disable pull ups should ¨be added.
:)

Re: Improper SPI levels on WIFI-Shield

Posted: Sun Mar 15, 2020 10:04 am
by iabdalkader
Yes but if you reset the camera, the pins will be floating. If you would like to add a function to disable the pull-ups go ahead and send a PR to github.