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8devices Community - View topic - Cannot connect through serial port
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View unanswered posts | View active topics It is currently 18 Apr 2024, 05:05



Reply to topic  [ 8 posts ] 
 Cannot connect through serial port 
Author Message

Joined: 01 Jul 2016, 21:08
Posts: 5
Hi,

I have a Carambola 1 with the breakout board, and I am trying to connect to it but failing.
Using the serial port:
1. Connected a a serial to USB converter to the female serial port connector (direct cable, no TX/RX crossing)
2. using picocom: picocom -b 115200 /dev/ttyUSB0
3. press the reset button on the breakout board

All I get is garbage (lots of weird looking chars) on the output (see the image). So either:
* the baud rate is wrong (tried the other most common ones like 9600 and 19200, same result)
* the voltage levels are wrong (I am using 5V, should I use 3.3V ?)
* some character mapping translation needs to occur (which one ?)

Any help would be appreciated, I am bit lost on how to get started with this board.


Attachments:
File comment: picocom output
picocom_output.png
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02 Jul 2016, 16:37
Profile

Joined: 01 Jul 2016, 21:08
Posts: 5
An update on what I have done so far:

1. the USB to Serial cable is crossed, I was wrong in my initial post
2. looking at the schematics of Carambola, there is a 3.3V <-> 5V level shifter on the serial port so this is not a voltage problem
3. I am 99,99% sure the board is working. When I connect an ethernet cable between its eth0 port and my PC (where I am running
a DHCP server) I see a DHCP lease shortly after boot and I can ping that address

Playing with different combinations of baudrate, data size, stop bits and parity I always get weird chars, so I thought it could be
a problem of charset encoding. The boards are designed by a company in Estonia, maybe they are using cyrilic or something
specific to that region.

So I opened the serial port with 8N1 and 115200 baud/s, and captured its output to a file after pressing the reset button on Carambola.
Then I tried opening that file with different encodings, without luck. Always giberish.

Now I am thinking I might be reading from the wrong serial port. Looking at the schematics, COM1 is connected to the DB9 connector.
Should I cut the traces and solder J10 and J9 so that I have COM0 instead ?


03 Jul 2016, 18:40
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Joined: 07 Dec 2011, 16:01
Posts: 525
Location: Lithuania
Hi,
do you have breakout board schematics ?


04 Jul 2016, 07:03
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Joined: 01 Jul 2016, 21:08
Posts: 5
Hi,

I got the dev board schematics from here: http://www.8devices.com/media/products/ ... ematic.pdf
I assume they are correct.

In the meanwhile, I am going to try with a different USB to serial cable. The one I have right now was hacked together from old
parts and might not be suitable for 115200 baud/s.


04 Jul 2016, 10:05
Profile

Joined: 07 Dec 2011, 16:01
Posts: 525
Location: Lithuania
Ok but this is original board developed by 8devices company not Estonian company.
Are you using serial cable USB <-> DB9 or USB <-> 3.3V TTL ?
Maybe something wrong with your USB converter cable ? Try another converter cable.
Firmware original from 8devices ?


04 Jul 2016, 10:35
Profile

Joined: 01 Jul 2016, 21:08
Posts: 5
I am using a USB <-> DB9 cable, but self-made and unshielded. It might be picking up noise.
The board firmware was not modified. I bought the board a couple of years ago but never got the time to play with it.

And I am sorry for confusing Estonia and Lithuania. I am a bit of an ignorant when it comes to geography and history.


04 Jul 2016, 12:18
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Joined: 07 Dec 2011, 16:01
Posts: 525
Location: Lithuania


04 Jul 2016, 14:02
Profile

Joined: 01 Jul 2016, 21:08
Posts: 5
Yup, it was the serial cable. Tried today with a proper, shielded cable, and it all worked fine.
Thanks for your patient and time.


05 Jul 2016, 17:15
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