> I am thinking of implementing an USB host on a data
> logging device and are looking at various method of
> doing it. My final intention is to attach a pen drive
> ( which are cheaply and readily available ) to the
> data logging device and remove it after a month and
> copy whatever data stored in the pen drive to a pc.
>
>>From information gathered on the net, it seems that
> most USB host are implemented on higher end micro
> processor. I intend to build the USB 1.1 host that
> will only access pen drive. I understand that i also
> have to write the interface for the FAT32. Any
> suggestions or ideas or valuable links?

Google for "on the go" and Philips. They have several USB controllers 
which allow easy slave / host / otg operation.
OTG is effectively what you want. Philips provide referenc ecode to 
get you going with almost all the complexity in the IC. I had a quick 
look at some sample code a while ago and it looked extremely easy to 
get going. No doubt a full design has complexity but most fot he USB 
details are invisible to you. Philips also do evaluation kits.


    http://www.semiconductors.philips.com/markets/connectivity/wired/usb/index.html

On The Go controllers

        http://www.semiconductors.philips.com/markets/connectivity/wired/usb/products/

One example

        http://www.semiconductors.philips.com/cgi-bin/pldb/pip/isp1362.html

General description

The ISP1362 is a single-chip Universal Serial Bus (USB) On-The-Go 
(OTG) controller integrated with the advanced Philips Slave Host 
Controller (PSHC) and the Philips ISP1181B Device Controller (DC). The 
USB OTG controller is compliant with On-The-Go Supplement to the USB 
2.0 Specification Rev. 1.0a. The host and device controllers are 
compliant with Universal Serial Bus Specification Rev. 2.0, supporting 
data transfer at full-speed (12 Mbit/s) and low-speed (1.5 Mbit/s).

The ISP1362 has two USB ports: port 1 and port 2. Port 1 can be 
hardware configured to function as a downstream port, an upstream port 
or an OTG port whereas port 2 can only be used as a downstream port. 
The OTG port can switch roles from host to peripheral, or from 
peripheral to host. The OTG port can become a host through the Host 
Negotiation Protocol (HNP) as specified in the OTG supplement.

A USB product with OTG capability can function either as a host or as 
a peripheral. For instance, with this dual-role capability, a Personal 
Computer (PC) peripheral such as a printer may switch roles from a 
peripheral to a host for connecting to a digital camera so that the 
printer can print pictures taken by the camera without using a PC. 
When a USB product with OTG capability is inactive, the USB interface 
is turned off. This feature has made OTG a technology well-suited for 
use in portable devices?such as, Personal Digital Assistant (PDA), 
Digital Still Camera (DSC) and mobile phone?in which power consumption 
is a concern. The ISP1362 is an OTG controller designed to perform 
such functions.



        Russell McMahon 

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