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Topic: Weird TTL Connection Issue on Linksys WRT3200ACM

The content of this topic has been archived on 7 May 2018. There are no obvious gaps in this topic, but there may still be some posts missing at the end.

(Correct me if its a common known issue or if I made some stupid mistake.)

Today I get my new WRT3200ACM and start to play around. Everything is fine until I try the USB-to-TTL thing:

I picked a TTL-USB cable which has been working perfectly with my old router (TP-Link wr1041n). I connected the cable with the router & PC correctly. However, when I turn on the power, 6 of the LEDs (the 2 for wifi & the 4 for LAN) blinked once and then all LEDs are off forever. The boot process looks like being "blocked" by something and nothing is transmitted via the serial port.

Then I saw #12 of the thread "Did I just brick my router? Linksys WRT1900AC" in this forum (I don't have the permission to put a link here, sorry) and realized that I'm facing exactly the same issue: If PIN2 (TX on the router) is physically connected to the USB-TTL cable before the power is on, the boot will be blocked. But if I keep that pin physically disconnected, turn on the power first, and then immediately connect that pin, I'll be able to get those regular information (uboot & etc) from the serial port.

The post above is a WRT1900 v2 and my unit is WRT3200ACM. At first I thought this to be expected for WRT series routers but a youtube video connecting a WRT1200 using TTL-USB proved that I was wrong.

The cable I'm using is "silicon labs cp210x usb to uart bridge". Not sure if that's the problem of the cable itself. Anyway, this seems weird. Has anyone seen this before?

(Last edited by swgr on 19 Feb 2017, 13:36)

I saw one more post with similar symptom, #77 of the 3200 main thread.

I have seen practically the same with Netgear WNDR3700. USB connection had to be made after powering the router. And to capture the early u-boot log you had to be quick.

I don't remember if it was just that TX,  but roughly similar in any case.

EDIT:
My USB-TTL cable is similar as yours, so this might be related to that.
I just checked it: silicon labs cp210x usb

(Last edited by hnyman on 19 Feb 2017, 14:22)

I tried to use my Arduino MEGA 2560 board as an USB-to-TTL and the same thing happened -- it works with my old TP-Link wr1041n perfectly, but for Linkedsys WRT3200ACM I must delay the connection of TX pin in order to boot the unit.

One more case found with a WRT1200AC:
zhuanlan.zhihu.com/p/25320124

Have any of you ever seen some strange characters like this ones? h_ttp://i64.tinypic.com/n65jj7.png
That's what I get from a Nanostation M5 using minicom with an RS232 connection directly to the COM port of my PC (/dev/ttyS0)

(Last edited by bawfree on 23 Feb 2017, 01:24)

bawfree wrote:

Have any of you ever seen some strange characters like this ones? h_ttp://i64.tinypic.com/n65jj7.png
That's what I get from a Nanostation M5 using minicom with an RS232 connection directly to the COM port of my PC (/dev/ttyS0)

Wrong baud rate?

swgr wrote:
bawfree wrote:

Have any of you ever seen some strange characters like this ones? h_ttp://i64.tinypic.com/n65jj7.png
That's what I get from a Nanostation M5 using minicom with an RS232 connection directly to the COM port of my PC (/dev/ttyS0)

Wrong baud rate?

I've tried almost everything, two nanostation M5 antenas, one briched the other one working fine, same behavior.

I'm using
sudo minicom -D /dev/ttyUSB0 -o -b 115200 -8

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