FT232RL interfacing with ATMega328 doesn't appear as a Comm port

Hello all,

I am trying to create my own Arduino for a certain application that can be left installed, but I'm having some issues. The FT232RL will not appear to the computer, it shows as an unknown device. I have narrowed down the problem but I need some help:

-It is not the USB cable, it includes the D- and D+ and works for programming other devices -It is not a driver issue as I have a ft232rl breakout board that works perfectly with my computer -The D- and D+ lines are reaching the pins of the ft232rl, confirmed with a multimeter -The ft232rl has its vcc supplied (5v) confirmed with a multimeter -The ft232rl grounds are supplied to all pins needing it, confirmed with a multimeter -The ft232rl works to a point, it does output 3.3v on its VCCOUT or whatever its called pin, confirmed with a multimeter, this means it should work completely as it should be completely fried if the basic hardwired components of the IC are working correctly

The Rx and Tx lines are connected to the AVR but even if the weren't I would think the FT232rl would still be recognized by the computer (I am not sure about this).

I am really stumped with this one guys. All power, ground, and I/O lines are reaching the IC. My thoughts on reasons for this error are:

-The FT232rl IC has not been pre-programmed with its USB enumeration protocols. I thought this was done at the factory so the engineer didn't need to do anything at all if they didn't want to. Please correct me if i'm wrong on this one. -A defective chip, but its not entirely defective if it is outputting 3.3v on its VCCOUT pin. However, this is probably just a resistor on the die and should't be affected if the software aspect of the chip is ruined.

I can upload my schematic if necessary, but I need a sanity check on this one. Is their something I just missed?

Thanks you guys, and btw this isn't my first post I just forget my username. Oops!

What is the physical form of the FT232RL? Do you have a link to its datasheet?

I have an FTDI cable that registers as a valid device (on Ubuntu) even if nothing is connected to the non-PC end of it. This is what I would expect.


I gather you are using your own custom PCB for mounting this FT232RL chip.

There are few things to go wrong in the design with this chip. There is no crystal to be wrong for one.

I would not worry about the factory configuration. I think you need to go over your design carefully, and ensure that all four ground pins and the "test" pin are grounded, and that VCCIO is connected to VCC as indicated in the datasheet, and that nothing else is that should not be connected.

It turns out I didn't know the test pin needed to be grounded. Thanks for your help, it works perfectly now. BTW doesn't it have an internal crystal that is suffice for most applications?

Well, you can mark the (original) topic as “Solved” then.

Apparently the accuracy of a crystal is not required for USB, so the internal CMOS clock is adequate. Possibly has some internal calibration and/ or compensation.