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Having trouble connecting to on-board serial port

Got problems with your B2 or B3? Share and get helped!
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minkanjin
Posts: 8
Joined: 04 Aug 2012, 18:41

Having trouble connecting to on-board serial port

Post by minkanjin »

I'm trying to access the serial port of my B3. I've followed the guide on the wiki, except that I'm using a pl2303 usb-to-serial converter. When I connect all I get is garble. Is the pl2303 incompatible or am I doing something else wrong?
johannes
Posts: 1470
Joined: 31 Dec 2006, 07:12
Location: Sweden
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Re: Having trouble connecting to on-board serial port

Post by johannes »

the standard problem when getting garble (then you are at least getting something) is that you set the speed wrong. You an also try resetting your terminal, since it can get out-of-sync. Third possible problem is that the ground wire is missing or poorly connected. Get back if you don't get it working. :)
/Johannes (Excito co-founder a long time ago, but now I'm just Johannes)
minkanjin
Posts: 8
Joined: 04 Aug 2012, 18:41

Re: Having trouble connecting to on-board serial port

Post by minkanjin »

Here is the settings I tried:
Baud rate: tried every setting from 300 to 927600 (including 115200, as suggested by the wiki).
Data bits: 8
Stop bits: 1
Parity: none
Handshake: tried both none and software

I've just spent some time to clean all the contacts on my improvised serial connector, but I still have the problem. The total resistance of the ground connector between the two devices is about 0.3 ohms, if I'm reading the meter correctly. I don't know if that is a lot; I don't normally work with hardware.
johannes
Posts: 1470
Joined: 31 Dec 2006, 07:12
Location: Sweden
Contact:

Re: Having trouble connecting to on-board serial port

Post by johannes »

Strange, seems you are doing it right. 115200 and no handshake is correct settings. Also 0.3 ohm is probably what you are getting if you would connect your meter probes directly together, so that's good.

Another thing would be if your serial - to - usb adapter has the wrong voltage, it has to work at 3.3V signalling speeds. Could that be it? Otherwise, try connecting hte TX and RX together at your USB serial adapter, and see if it echos. Then you can do the same with the B3 to check. Hopefully this brings you closer to the issue.
/Johannes (Excito co-founder a long time ago, but now I'm just Johannes)
MouettE
Site admin
Posts: 341
Joined: 06 Oct 2011, 19:45

Re: Having trouble connecting to on-board serial port

Post by MouettE »

Hello,

The PL2303 is a converter between USB and standard RS232 serial port. It is not compatible with the TTL 3.3V console port on the B3. You need to use another adapter, such as the FTDI TTL-232RG-VREG3V3-WE, available in sereral online shops.
minkanjin
Posts: 8
Joined: 04 Aug 2012, 18:41

Re: Having trouble connecting to on-board serial port

Post by minkanjin »

Thanks. I added a max3232 to convert the voltage levels and it's working now.

Unfortunately, the max3232 requires a 3.3V source (currently I'm using an external source). Is there an open solder-able contact point on the B3 board that would supply 3.3V?

This is just for convenience sake; if it's not possible to get the power internally, I can just continue using the external source.
minkanjin
Posts: 8
Joined: 04 Aug 2012, 18:41

Re: Having trouble connecting to on-board serial port

Post by minkanjin »

Hopefully everyone is back from holiday. Is there any response for my question above? (Is there an open solder point on the B3 board that would supply 3.3V?)
pompopom
Posts: 50
Joined: 13 Dec 2012, 16:45

Re: Having trouble connecting to on-board serial port

Post by pompopom »

max3232 can also handle 5V power supply and lucky for you, this comes right from your USB port :-)
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