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Beagle 12 for Serial Debugging?
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Beagle 12 for Serial Debugging?

by jleeman on Mon Jul 02, 2018 12:12 pm

Hey all - I've got an old instrument (RS232) that is hooked up to a host computer via a USB adapter. I'd like to record the commands the computer sends (ASCII serial 9600 baud) to the unit and it's responses to back out the command set. While I don't necessarily need a protocol analyzer for this, would the Beagle do the job or is there another tool that would be more suited? I'm looking for a plug-in-line device as adding software to the host is not an option, neither is opening up the instrument. Thanks!

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Re: Beagle 12 for Serial Debugging?

by adafruit_support_mike on Tue Jul 03, 2018 12:59 am

Hrm.. as long as the 9600 baud ASCII is in the right voltage range (0V-3.3V for a BBB), the only real problem will be clock synchronization.

Serial connections work on the assumption that the devices at both ends have synchronized clocks. Ideally, the receiver reads its RX line half a clock tick after the sender sets its TX line.. if we call the period of a 9600 baud connection 104us, the sender would set TX at 0us, 104us, 208us, etc, and the receiver would read the line at 52us, 156us, 26us, etc.

I'm not sure how well a BBB would sync its RX to a line where it only listens passively.

It certainly won't hurt to try, but you might want to use a microcontroller instead. Let the chip watch the RX line and spot the high/low transitions, extract the clock timing from that information, and then start interpreting characters. Then the microcontroller can copy that information to an SD card, a display, or a Serial connection that goes to a desktop computer.

An alternative would be to try a Saleae logic analyzer:

https://www.adafruit.com/?q=saleae

They're not cheap, but they're quite good for medium-speed sampling. The device pipelines data to a computer, so its storage is effectively infinite, and the software has a good set of protocol analyzers waiting to be used.

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Re: Beagle 12 for Serial Debugging?

by jleeman on Tue Jul 03, 2018 1:07 am

I'm thinking of your Beagle 12 usb analyzer, not a BBB.

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Re: Beagle 12 for Serial Debugging?

by adafruit_support_mike on Tue Jul 03, 2018 11:30 pm

Ah.. you mean catching the signal after it's been converted to USB. That's doable, but would be more complex than monitoring the signals after they've been converted back to Serial.

Do you have access to the Serial side of the USB-to-Serial converter?

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Re: Beagle 12 for Serial Debugging?

by jleeman on Wed Jul 04, 2018 9:31 am

I do, but I'm going to have limited time to work on the equipment so I'm looking for a plug and play solution ideally and software on the host machine isn't an option.

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Re: Beagle 12 for Serial Debugging?

by adafruit_support_mike on Wed Jul 04, 2018 9:54 pm

The Beagle USB analyzer and the Saleae logic analyzers will both be non-intrusive as far as the machines at either end of the Serial connection are concerned.

The Beagle USB analyzer is a pass-through device, and the Saleae logic analyzer has high-impedance probes that will clip onto the TX and RX lines and track their voltage. Both require a computer to run the analysis software, but that machine is independent of the ones you want to examine.

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Re: Beagle 12 for Serial Debugging?

by jleeman on Thu Jul 05, 2018 10:54 am

I guess my question, most simply stated is: I don't really need a full USB protocol analyzer for this job, will the Beagle 12 let me simply display only the serial data being sent/received? Their software looks very powerful, but I don't need all of the details of the USB transaction.

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Re: Beagle 12 for Serial Debugging?

by adafruit_support_mike on Thu Jul 05, 2018 11:06 pm

No, it will only show you the USB transfers. The Serial data will be in there, but you'll probably have to do some extra decoding to get anything but the binary values.

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