Hacking USB Serial Ports
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Fig 4 - View of the completed hack
And that’s pretty much it. From start to finish, this hack will probably take you an hour or so including the time required to research an unknown device. As a special bonus, here’s a device that didn’t even have any markings on the controller chip so it was impossible to look up the pinout online. We used the steps outlined above to trace it out, applied a few toggles to each of the pins on the level shifter to determine RxD and TxD, and boom - another device hacked. This one was cheaper than the keyspan - $10 vs $20 if memory serves, but just as hackable.
Fig 5 - Hacked No-Name USB Serial Adapter with Unknown Chipset
Bonus #2:
Some of you may be wondering about taking over the microcontroller in the adapter. Sure you can! It’s a topic for another article so I won’t discuss all the details here, but you can freely download the TUSB3410 development tools from TI. By forcing the device to use the TI driver instead of the generic RS232 port driver, you gain access to the flash memory and are free to write new applications and upload them to the device. Enjoy!
September 23, 2009 @ 2:11 pm
[…] The folks at Openschemes.com have written up an article on how to convert a USB serial port adapter to a low voltage serial interface for interfacing with microcontrollers. Though you can always just buy one, this is a fairly quick and cheap solution, especially if you are in a pinch or don’t have access to a retailer. The specific models you should watch for, are the two chip ones.They go through the process of finding exactly where to patch in to add an extra interface. It only takes a couple wires and you are ready to go. […]
October 5, 2009 @ 1:55 am
I want to say - thank you for this!