4.1 Ethernet Reset U6 pin 5, can I tie into this for a system wide reset?

[japreja]

I am in need of a reset pin, and although any pin can technically be used and coded, The DP83825 IC (U6) shows RST on its pin 5. If there is no exposed Test-Point or pad for this pin, due to SMD components, I am comfortable in gently scraping away some of the trace coatings and soldering.

I am assuming that when the Teensy is reset, when programming, this RST line is activated. Is that a safe assumption? If so which IC is the U6? and its orientation? and can you point out the trace that I would need to tie into? Is the signal strong enough to be tied to additional chips?

Or do I have it all wrong in that the U6 IC is activating the reset and not the actual Teensy U1 IC?

Thank you!

 

[Frank B]

That pin is connected to a GPIO on the Teensy-CPU.
It will not reset anything but the DP83825.

 

[Frank B]

I think the name of signal you want is POR_B ( correct me please, if i'm wrong, Paul )
It is connected with the bootloader-cpu, PTB1.
I don't know how the bootloader gets its reset. Maybe with a watchdog. Or there is no reset.

You may want to download the datasheet of this CPU to see where PTB1 (Pin 9) is.

Edit:

Pin 9

 

[PaulStoffregen]

I am assuming that when the Teensy is reset, when programming, this RST line is activated. Is that a safe assumption?

Nope, completely wrong assumption. Frank's explanation is correct.

I think the name of signal you want is POR_B ( correct me please, if i'm wrong, Paul )
It is connected with the bootloader-cpu, PTB1.

While this is technically true, the MKL02 always drives that pin. It is *not* open collector / drain as we have on Teensy 3.x. If you try to drive it, you'll conflict with the driver in the MKL02's PTB1 pin.

If you wire up logic or a switch to safely force PTB1 low without harming the MKL02 PTB1 pin, you may end up confusing the firmware on the MKL02 chip. It may not recover to a usable state without power cycling. Whether anything "bad" happens, I can not say with any certainty. The behavior should be considered "undefined".


To achieve the reset behavior you want, I'd recommend exploring the IMXRT external watchdog feature. It's documented in the reference manual, chapter 59 starting on page 3213.

https://www.pjrc.com/teensy/datasheets.html