Hi Neil,

I can tell you that you may not use the USB logo just because you use one of these chips. If you want to use the USB logo you have to spring for your own VID and PID through usb.org, and then submit your device to them for compliance testing. Only after they've certified your product will you be allowed to display the logo on your product.

If you don't want to use the logo, you can use SiLabs' VID. Moreover, if you contact SiLabs they will assign a unique PID for your product.

As for the two chips, I use SiLabs CP2102. It requires notably fewer external parts to work. For example, the CP2102 has its own internal clock and doesn't need a crystal. In point of fact, the only external parts I use are an LED and resistor to show that it's initialized, a 4.7 µF tantalum cap, and a USB jack to plug into. Of course, if you want, it'll handle the full compliment of RS232 signals, but I don't want.

The big drawback to the CP2102 is board assembly. It took some special hardware and quite a few attempts to learn to solder one of these little things.

Comparatively, it's a piece of cake to solder the FTDI chips. So I tried to use one, but only once. The crystal didn't want to oscillate, which I understand is a common issue with the FTDI chips. Now I'm sure that if I had spent some time doing so I could have gotten the chip to work, but it still bothered me that it was so persnickity. At that point I was concerned about reliability issues. Since I had already solved the problem of soldering the CP2102 I dropped the FTDI after only the one attempt. Still, I may revisit the choice at a later time.

As for programming, SiLabs of course provides a (royalty free) driver that acts as a virtual com port, but they also provide an API and driver (USBExpress) in the form of a DLL that you can "include" in your program. USBExpress lets you program directly to your device without dealing with Windows drivers, DCBs and such. It's much simpler than programming to a com port. I strongly recommend that you check it out.

FTDI may or may not provide a similar utility. I don't know since I never got that far using their part. I suspect, however, that they have to just to be competitive.

Joe