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Topic: serial port on netgear DG834G v4

The content of this topic has been archived on 23 Mar 2018. There are no obvious gaps in this topic, but there may still be some posts missing at the end.

Has anyone successfully located the serial port on a Netgear DG834G v4 board ? 

I've got a few of these and I've tried on more than one board to find the serial output with no luck.  I think it must be either J525 to the left, or J521 to the right of the BCM6348 but I can't seem to get any output from either of these.  Here's the board in question :

http://wiki.openwrt.org/_media/oldwiki/ … 834gv4.jpg

Perhaps I've not got the right serial settings or the pinouts are not as I expect.  I'm using a FTDI 3.3V TTL to USB cable which, I must admit, I've only ever used on AR7 based routers before, so I'm not even sure it would work with the broadcom chips ?

If anyone can clue me up that would be great !

UART 3.3V to USB will definitely work on Broadcom. I tried it on some D-Link modem and Profilic adapter.
For searching UART you can use multimeter: ohmmeter for GND<->GND and +3.3V<->+3.3V and voltmeter for Tx. During boot it will have voltage ~1.6V, and in idle state +3.3V. Then you can connect computer Rx and test various speeds for valid data. If is this succesful, last remaining pin is modem Rx.

hi pc2005,

Good to know I've got the right cable.  I did have a poke around with a meter and J521 has a ground but I can't find the tx.  My crappy analogue meter is probably not up to the job though !  I guess I might need to go out and get a new meter ...

~1.6V on UART are only when some pseudorandom is transmitted (digital multimeter is too slow to sample correct value, analog is similar). Data transfer is only about boot time (if you have linux on it, you can sometimes do something like cat /dev/urandom > /dev/ttyS0). But you can search Tx even if you have not working multimeter. Just try every pin on board with Rx wire to computer (if you connect rx-rx, or rx-gnd... nothing happens).

P.S. did you found Vcc pin? (first ohmmeter wire on header and second on some IC supply - best DRAM or flash, with unconnected board of course :-D).

There's no vcc 3.3v line on either J521 or J525, according to my analogue meter, and no discernible line with 1.6v or 3.3v during/after boot. 

On closer inspection of J521, two of the tracks appear to run away to surface mount pads with no components (R522 & R523) and are thus not connected, so I don't think this could possibly be a serial port. 

All three non-ground pins of J525 appear to run directly to the broadcom CPU, so am I right in thinking this is more likely to be the console ?  I've tried many permutations of speeds/bits/parity/flow control on my terminal, across all pins on J525 but still no output. 

There are no other obvious (to me at least) connectors that could be a serial port on the board, so perhaps Netgear just left it disabled ?  I see what I think is a JTAG on J201, so maybe this is all they thought they needed to include ? 

Going to try on replacement hardware today, just in case, but any further suggestions would be useful. 

Pc2005 your help is greatly appreciated !

According this page http://pudeev.livejournal.com/37410.html , uart seems to be in right middle side of chip. So it seems to be J521. I think 3.3V on uart is not required, so it can be GND, Tx and Rx.

You can try measure for output on J201. I could be there too.

thanks a lot for the link, very helpful smile   J525 tracks run into top left of the chip, so this is clearly not it.

J521 is definitely not connected, so you're right, the only place left to look is J201.  I'll let you know how I get along.

Thanks once again.

For the reference of anyone reading this, I'm actually working on a DG834v4 (no "G" - it's the board without wireless) and not a DG834Gv4 as I originally suggested.

I actually opened up a Netgear DGN2000 and it is a very similar board, and also uses the BCM6348SKFBG part.  It also has a J521 in the same place as the DG834v4, and this is definitely the serial port on the DGN2000.  Pinout is -

1 - GND
2 - Tx
3 - Vcc
4 - Rx

115200/8/N/1/no flow control

The components around J521 which are missing on the DG834v4 are present on this board (R521 and R523).  I'm not sure if this is a multilayer board, but there are no tracks on either visible surface to pin 2 on the DG834v4 either.

I haven't had a poke around on J201 yet, but given the above do you think it is worth it pc2005 ?

It is with high probability multilayer board. J201 is maybe JTAG, so it can be useful too, but if another board has uart  on same J521 on same place, then it will be probably uart. Is uart on DGN2000 connected trough some resistors? You can connect resistor with same value as on DGN2000 and poke on R521 and R523 pads (it could be less than 10 kiloohm or even zero).

P.S. Rx for board is close to edge of chip, so it's maybe accessible with thin wire connected to ohmmeter. But this is very dangerous test :-).

Hi all,

Just a bit of feedback since my last post on the DG834v4 serial port issue...

Thanks to pc2005's sage advice, I found that the RX and TX pins were indeed connected through 1k resistors on their way to the BCM chip, on the DGN2000 at least (pads R521 and R522).   

On the DG834v4 these pads were unpopulated.  The good news is that soldering on 1k resistors to these pads results in a fully functional console, with the same pinout on J521 and port settings as the DGN2000.  Hooray !

Sadly, during this exercise, two bricked DG834v4 were irrecoverably damaged by my cack-handed soldering, and have since been thrown in the bin.  It's very easy to tear a surface mount pad away from the track whilst soldering so take care if attempting this at home.

Hi,

Cheers for the feedback - I've just picked up a GD834v4 (UK) and managed to brick it big_smile

Would it not be an idea just to bridge the two solder points (R521 / R522) and put 1k resistors in-line before the serial port level converter (MAX232 in my case) ? Am I missing something obvious / dangerous there ?

Thomas.

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