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USB to TTL Serial Cable Not Working

by brianp1 on Sun Feb 10, 2013 7:39 pm

I have been trying in vain to get the USB to TTL Serial Cable to work with my new Raspberry Pi. I have followed the tutorial and have been unable to get it to work.

In Mac OS X, 10.8.2, I have installed the Lion-compatible (said to also be Mountain Lion compatible) open-source PL-based drivers from http://www.xbsd.nl/2011/07/pl2303-serial-usb-on-osx-lion.html. I have used both minicom and ZOC, and the most I can get from the serial cable are endless garbage characters.

I tried with a Windows XP machine, and amazingly, I was able to receive from the Raspberry Pi (though oftentimes, the output would be mangled); however, I cannot send to the Raspberry Pi (typing has no effect, sending resets, etc.). It is as though the Pi is not actually receiving anything from the cable.

I am trying to determine whether the cable or the Pi is to blame. I can attempt tomorrow to connect the serial cable to a DB-9 plug and connect it to a linux box to see if that works.

I haven't put the RPi through any tests yet, other than booting into the OS (I have tested with both Wheezy and Occidental). The RPi has had some other issues with random shutdowns, etc., which leads me to wonder whether the RPi unit is to blame.

Any suggestions? Thank you for your help.
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Re: USB to TTL Serial Cable Not Working

by adafruit_support_bill on Mon Feb 11, 2013 6:33 am

the most I can get from the serial cable are endless garbage characters.

Are you sure that the baud-rate was the same on both ends?
I can attempt tomorrow to connect the serial cable to a DB-9 plug and connect it to a linux box to see if that works.

Don't connect it directly to an RS-232 serial port. The RS-232 signal levels will damage the TTL cable.

Any suggestions?

Try a simple loop-back test. Connect the Tx to the Rx and see if what you type is echoed back.
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Re: USB to TTL Serial Cable Not Working

by brianp1 on Tue Feb 12, 2013 1:11 am

Thank you adafruit_support for the reply.

I did confirm that both the serial terminal program and the getty server on the pi were both at 115200.

Thanks for the heads up that it is not an RS-232. I did not hook it up to anything (I was too lazy to find a serial plug anyhow).

I did the loopback test, and I cannot get any response, which seems to confirm that the transmit is not working. Interestingly, connecting it to the mac spewed an endless string of garbage characters, so there is an issue with the driver or the interface with the TTL cable.

It would appear that the TTL cable does not work properly. How do you suggest I further test or move forward?

Thank you for your assistance.
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Re: USB to TTL Serial Cable Not Working

by adafruit_support_bill on Tue Feb 12, 2013 6:52 am

Which model cable is this?
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Re: USB to TTL Serial Cable Not Working

by brianp1 on Tue Feb 12, 2013 2:07 pm

It is the one that came with the Raspberry Pi Starter Kit https://www.adafruit.com/products/1014. I just received it a week ago, so it is the current version, I imagine.

Cheers
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Re: USB to TTL Serial Cable Not Working

by adafruit_support_bill on Tue Feb 12, 2013 2:25 pm

OK. Contact support@adafruit.com with a link to this thread and ask for a replacement cable.
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