Help identifying UART pins

This is DNA Valokuitu Plus-Modeemi EX400 sold at least in Finland by operator DNA. It's a SoC Type: MediaTek MT7621 ver:1 eco:3 and it's got a fork of Openwrt inside it. I am trying to locate UART pins but it's not obvious to me. Any help is appreciated. Am I correct assuming JTAG is not good for interacting with u-boot and tfpt loading images?


There are three pins left of the white connector on the bottom right hand picture but they are so tiny (1.27mm pitch) that I have not been able to reliably connect anything to them yet.


I'd use a volt meter, and connect the probes to the pins while switching on the device.
Assuming one of the pins is GND, one of the other two should have the voltage fluctuate,
which could indicate it being Tx.

Oh yes, I did that. One if them is ground and the two others measure to 3.3V so it's promising. Measuring one way the 3.3V pins offer infinite resistance and switching the probes it gives some -14 ohms. Dunno why it's negative, maybe my cheap volt meter or I don't understand what is being measured.

It's just that I tried connecting wires to all of them and didn't get much anything from console. I have a ttl-serial level switcher in between. I am in hopes someone could identify another likely spot for the pins.

pretty sure the Rx is supposed to be 0.

then I'd try the 14 pin connector. by the USB port.

I took it for JTAG but I'll give it a go. :slight_smile:

What about the black socket just next to the red ethernet connector?


Bingo! That's it. I never realised it's a connector of any sort. Thank you very much. :smiley:

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