Hi, I'm new here. How's everybody doing?

I have a strange case of my WR841N v8.4 not talking properly via Putty with my PC. I'm using USB-TTL serial interface on CH340G and only listening seems to be working fine. I checked all cables, plugs, connections under magnifying glass and traced them to SoC and verified there is a signal (with a beep on multimeter). I checked CH340g as well - all OK.

Baud I'm using is 117000, 7N1 - yes, that's 7bits-often case with ch340.
When I disconnect Rx router side, I can read console on 115200 without artifacts.
With both lines connected I get:
[Links here - can't post yet]
115200: imgur_com/a/2L6AM
128000: imgur_com/a/lDTWS

I read somewhere about pluging in multimeter between Rx and Gnd and it seems to have helped a bit as I'm able to interact with router but still cannot enter 'tpl'. Interaction is allowed after booting process, when whatever I type in I get asked to authenticate with a login and pswd-tried admin/admin and root/5up-nothing works but at least I get information back that credentials were invalid - Tx(PC)->Rx works

Vcc not connected ofc.

I figured I make some more measurements, just in case. Maybe someone will have any idea what to do.
Pins on router have: Vcc-3.3v; Tx-2.52v; Rx-3.03v with USB-TTL connected and ACadapter ON.
Impendence between pins: Rx-Gnd - 725 Ohm; Rx-Vcc - indefinite; Tx-Gnd - 722Ohm; Tx-Vcc - 82,5kOhm

Do I need to use a pull-up/pull-down resistor? I know it has not been the case on my build but who knows? What are your voltages on the pins?
Maybe Rx is not Rx?

Can anyone help? Thanks a bunch

(Last edited by meekowai on 21 Nov 2017, 17:06)

Your connection setting is pretty weird, better use the standard 115200 8N1.
If you get some proper feedback of your input when the system is fully booted, then you probably have a usable connection over all and it is just a matter of bad timing to enter uboot. It took many of us a couple of tries to succeed on that, and one good solution is copying tpl to the clipboard and then just rapidly hit the shortcut keys for pasting its content.

Finally I was able to connect.

!! I shortened my cable from 30 to 15 centimeters !!
Nowhere have I found information about the cable length and to keep it to minimum. Thought 30cm shouldn't be an issue.

Baud still needs to be 118000 - otherwise it's unreadable. I guess it has something to do with CH340G baud accuracy +/-5% according to datasheet. Rest is 8N1.

Now the 'tpl' is catching correctly.

Issue solved...for now

(Last edited by meekowai on 22 Nov 2017, 09:01)

Because it usually isn't.

First of all, you should never connect -- and never have to connect -- VCC. In layman's terms: The difference in voltage between what your router already carries on VCC and what your adapter supplies on VCC can cause all kinds of havoc, from an unstable connection to a dead device.

If that's not the problem, one of the parts in your setup is not working in an ideal way, either your router, the adapter, or the port that's working your adapter.

You should get rid of that CH340 adapter and get a working one - like one from FTDI.

It's working for now. No reason to trash it.