Hello,
Most posts start by pointing out the fact the OP is new, so I will do the same ....I'm new to hardware 
I have played around with the Arduino and got a few basic projects working. I would like to connect my Arduino to a USB device that is a virtual com port. If i purchase the USB Host shield from somewhere like sparkfun, would it be possible for the USB slave drive to send data through to the USB host shield and manipulate this data via the Arduino?
Cheers.
Do you want to send data between a virtual com port on a computer and an arduino? Or are you thinking of trying to use the arduino to host a usb hard drive?
Or you're thinking to connect a USB-SerialConverter over a USB-HOST shield to arduino??
Hi Donghat,
From your description, it sounds like the device you want to connect presents itself as a virtual COM port when connected via an associated Windows or Linux driver. If that is the case then it is very likely the USB Host Shield will allow you to connect that device to the Arduino.
The important thing to understand is that the Virtual COM port is a feature of the USB Driver in the host. With the host shield, you have to make your own drivers. This means making a driver which talks to a specific USB serial device. The device may be of a number of types (CDC, Prolific, FTDI, ..) and you driver will have to be written for that specific device.
First check out the circuits@home web site and use the described there utilities under Windows or on the host shield to find details of descriptors fo your USB device. If the device is one of the common documented types, then a driver should be no problem. I put some code on circuits@home for driving the FDTI device already.
Let us know when you have the device descriptors.
From your description, it sounds like the device you want to connect presents itself as a virtual COM port when connected via an associated Windows or Linux driver
Exactly!
Thanks for taking the time to reply. I will investigate the type of device I wish to communicate to. I am fairly sure it is of type CDC, do I need further information than that? such as manufacturer? Would the manufacturer document how to communicate with the USB device?
I will try to get more information.
Thanks again.
If it is CDC, then you should see that class in the descriptors for the device.
I not aware of any existing USB Host shield driver for the CDC class, but it is worth asking on the circuits@home site.
The good news is that CDC is the most documented and most commonly implemented serial device. The down side is that it also the most complex!
Look for existing USB host examples for CDC from chip suppliers who have processors with USB Hosts (Atmel, Microchip, NXP), which might be adapted.
Hi All,
I have CDC ACM, FTDI and PL-2303 code working in the next major release of USB Host Library (with a bit of luck, to be released in a month or two).
Oleg.