Tuesday 22 November 2016

Test your USB serial converter

Back in the days

when PCs came with serial and parallel ports, techs had sets of plugs to test the serial and parallel interfaces with.

There is also a >>>video<<< on this!


I still use a RS232 adapter on my SurfacePro at work to configure Cisco network components. I had quite a few of these for the last few years with different chip sets.

For my microcontroller hacking joy, I have come to like CP2102 based adapters like this one. The chip is 5V tolerant and puts out 3.3V levels which is good enough for 5V applications, too.

Put it to the test

Sometimes, when stuff doesn't work as expected, I wonder: Does my USB-serial adapter even work? And the test is easy:
Simple loopback
On this adapter, we don't have any additional signal lines that we find on a fully featured adapter, so all we have to do is to connect the TXD pin to the RXD.
Now everything transmitted through the TXD pin is fed back to the receive pin.

If the driver installed ok, you will see a new COM Port. In this case: COM3

For the loopback test, you have to configure that COM-Port into Putty:
Configure Putty
By default, Putty has local echo off. That means that if you press a button on the keyboard, you will see nothing, unless something is sent back by the adapter.

If you see what you type, everything is ok:

No local echo

If you enable local echo (tick "Force on"),

Enable or disable local echo
you will see every keystroke twice:
With local echo
And that also means that your adapter works ok.

Materials used in the video and for the blog entry:

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