If you take off just the back cover of a Moto E6 phone most of the electronics is still covered.
But there are five little holes with a contact on the bottom.
Three of these test points measure ground, at least when I looked at them.
Two of them have this strange 4 level signal at a 2.5 V logic level.
The rate of the 12 pulses is 150 kHz.
The repetition of the chunks is 3 kHz.
What the heck is this?
(This is while the phone is operating normally.)
My first instinct was poor probe technique, but the signal isn't extending below the 0V level so, grounding may not the the cause here. The peak and fall to a lower level looks like pre-emphasis but that is a lot of premphasis for a low frequency signal, so probably not for a wired signal. 150Khz is awfully close 156Khz that some RFID operates at. Is there an antenna in the back cover of the phone with contacts to reach these pads?
Is there an antenna in the back cover of the phone with contacts to reach these pads?
Nope, but that's a good guess.
The back cover is plain plastic. It would have to have needles to interact with these points.
There's no charcoal gray stickers or gold contacts or anything.
I certainly looks like some kind of sync signals, there's never any data on it.
If we call the levels 3, 2, 1, 0, then 3 and 0 although they kind of look like preemphasis are distinct levels.
If it were something RF-ish, why would it idle at level 2 at the end of the burst before going to level 0?