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I got the FTDI UMFT201XB USB-to-I2C module in order to interface with an I2C peripheral through a USB port on my Windows 7 computer.

The VCP drivers seem to install correctly, and a COM port is assigned to the module, and can be opened by a terminal emulator. However, I cannot seem to get any signal in or out of the module. That is, I see no activity when I send data through the port, or receive any data when I connect an I2C device to it (this was debugged using a scope). I have also verified that the RESET isn't on.

I found very little helpful information out there on how to get this module to work, so if anyone has experience with it, or with similar FTDI modules, my question is: what are the steps that I need to take in order to get the module to communicate?

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    \$\begingroup\$ How are you trying to initiate I2C communications? By sending data through the COM port? I believe that is not how its done, you need to install the other "D2XX" driver and use the provided DLL where there should be some function calls to perform I2C functions: ftdichip.com/Support/Documents/ProgramGuides/… I considered using their solutions for USB-I2C bridge in the past but was also frustrated by their lack of support documentation and ended up making my own instead. \$\endgroup\$
    – Jon L
    Commented Aug 31, 2012 at 21:47

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The FT201X chip used on this module implements I2C slave mode only -- by default it does not operate as an I2C master. In other words, it is meant to be an I2C peripheral, not communicate with one.

In the datasheet, it does state that you can reconfigure the SCL and SDA pins as GPIO, which I suppose would allow you to bit-bang an I2C master implementation in software on the host, but it hardly seems like it would be worth the trouble.

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  • \$\begingroup\$ Not sure what I'm missing here. I take it that the module is meant to bridge between a USB device and a I2C peripheral (otherwise, what's the point?) All I want is to be able to communicate with an I2C peripheral through USB using this bridge... \$\endgroup\$
    – Saar Drimer
    Commented Aug 31, 2012 at 22:32
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    \$\begingroup\$ To be honest, I'm not sure I see the point, either. My guess would be that it's meant to allow an embedded processor (the I2C master) to communicate with a USB host in order to provide, for example, a user interface or maybe debugging information. \$\endgroup\$
    – Dave Tweed
    Commented Aug 31, 2012 at 22:58
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    \$\begingroup\$ To do what you want, you need something more like the Aardvark from Total Phase. I've used this product before to talk to an SPI slave device I was developing. No doubt there are cheaper options out there, too. This particular one comes with a very comprehensive user interface. \$\endgroup\$
    – Dave Tweed
    Commented Aug 31, 2012 at 23:02
  • \$\begingroup\$ +1 for Aardvark. The only downside to these devices are if you blow them up, TotalPhase expects you to buy a new one (no repair service) so I had to reverse the schematic and repair some myself. \$\endgroup\$
    – Adam Lawrence
    Commented Sep 1, 2012 at 12:20
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    \$\begingroup\$ Dave Tweed is exactly right -- the FT201X is an I2C slave only. It's meant to be a I2C peripheral that provides the master with the ability to send and receive a simple stream of bytes over USB. \$\endgroup\$
    – Jim Paris
    Commented Sep 1, 2012 at 19:01

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