Wiz812MJ Gets Hot when SPI is connected


I just got my Wiz812MJ ver 1.1.

The module get hot as soon as I connect SCS from my microcontroller.
If the module is just powered, it is warm.

I connected a second unit. It gets very hot just powering it.

Is there a mistake it the 812MJ datasheet pinout ?


Maybe you did a mistake in connecting it? How do you do it?

Where do these modules come from? May it happen that they are defective?

W5x00 chips become warm when PHY is connected. Not hot, but warm.

Do the modules function from any side - MCU or Ethernet?


Appreciate your response.

That is very possible.

With the RJ45 facing away from me, I expecting J1 on the left, and J2 on the right.

From your answer, I am assuming your Wi812Mj is not getting hot.


I do not have this module, but I use W5100 heavily. I am sure your module is designed using standard circuit.



I got a couple of Wiz810sio modules.

These don’t get hot, and am able to talk over SPI to it.

When I write the MAC address Byte 1 is the same as Byte 2. Is there something special I have to do to write MAC address?



Seems this module is broken then. If you put it into the same conditions as other modules and use the same software, and it behaves differently.

I do not think it is any issue with circuit as it could be if you use parallel access to the chip. You use SPI, and it sounds like chip is having problems. Anyway, the obvious things to check with the board are: (1) physical inspection if nothing is damaged or shorted; (2) power measurement before and after the regulator. I am afraid there’s not much more you can do… (considering you really put it into the same conditions as other modules!)


You are right. Learning the nuance of a new chip is always interesting.