I have not specifically tried the driver for the TTL232R cable to see how well that would work. The chip used in these cables (the FT232R) is a standard device from FTDI and if you use the driver in the D2XX direct mode instead of the VCP (virtual comm port) mode you get some options. When used in the D2XX mode it is possible to use the FT232R in a number of non-serial-port modes. If I recall correctly, from the chip data sheet, one mode would be GPIO on the individual pins.

This is rather more interesting on the TTL version of the cables as opposed to other adapters that also include an RS232 transceiver and end up with the +/- voltage swings on the output pins.

One problem that I do know of is that you must follow some special steps to enable cables for use in the direct mode. If you do not take these steps the Windows plug-and-play USB driver installation process will try to recognize the cable as a serial port device and install the VCP mode. If you have discrete hardware attached to the FT232R in this mode the I/Os will do some annoying turning on and off one or more times as the drivers are installed. This could put your device in a state that you did not anticipate.

So what one has to do is to take some steps to make it so that only the D2XX direct driver and DLL interface is active for the cable. FTDI has a couple of detailed App Notes on this subject that one can follow. One of those steps I believe is to re-program the PID code string in the chip so Windows will not see the FT232R as a standard serial port adapter device. FTDI has a procedure available where you can purchase PIDs from them for use in your own products. For small operators or experimenters they even offer up to 8 PIDs for free (all you have to do is ask) that you must use in conjunction with the FTDI VID.

I really intend to do some experimentation myself getting a special PID (and maybe even a VID through my company) and observe the benefits and tradeoffs of using the D2XX direct mode driver interface. It is just available time that has held me back from doing this. One issue of going this route is using different VID and PID codes, whilst you can still use a modified version of FTDIs driver release, you give up the stamp of the Microsoft WHQL certification which certs the drivers as "signed" and approved for use with Windows. If you want to have a signed driver you have to engage on your own with Microsoft to get that WHQL certification. A process which costs some $$$ and can be a PITA depending upon how you look at it. FTDI is willing to help and makes a good bit of information available and provides the tools needed to make it all happen. It's just been time and lack of financial incentive that have kept me from investigating this in depth.

In the several projects I've done where I've embedded the FT232R chip directly into the hardware design it has been more than adequate to use the VCP mode and the off the shelf (actually off-the-web) driver from FTDI to interface the device in the VCP / serial port manner. Its like --- taking the shortest path to solution. :-)

Michael Karas