Although I understand that there have been some new chips come out
recently, from what I have seen and from research I did about a year
ago, the host mode side of USB is very difficult to implement.  The
problem comes down to the fact that Windows and USB grew up together.

Although there are "host mode" chips used inside of PCs to connect
the computer to a USB slave device, the host chip controls only the
physical characteristics of USB communication.  The intelligence needed
to actually operate a USB link is embedded in Windows.  The host chip
is not very smart as it only does what Windows tells it to.  As such,
most of the intelligence needed for a USB link lives on the host side.
Since Windows can be as bloated and inefficient as Microsoft feels like
making it, the host side intelligence is fairly complicated, whereas
the slave side is much simpler by comparison.

So, since Windows runs most things USB and small cheap devices are on
the slave side, slave chips are plentiful and fairly easy to use.  Host
controller chips that don't need Windows and a PC are almost non-existent.
Even so, an (intelligent) host controller chip is still going to need
a fair amount of software smarts to run a USB link.  From a design
standpoint, using an intelligent host controller chip will not at all be
a simple "plug and play" arrangement by any stretch of the imagination.

In building projects some of us want to do MIDI connections, computer
to scanner or roll punch or other types data connections.  And although
USB is all the rage these days, from a design standpoint, unless you
are going to be building a million units of something it is not
necessarily the easiest way to make a data connection.  RS232 (computer
serial port) is much simpler to implement.  Also there are a number of
very easy to use RS232 chips that can be use to make a very reliable
data connection without needing any link controller software.

What it really comes down to is that using RS232 or MIDI is a simple
matter of connecting up the chips and pumping data through them and
you're done.  Setting up a USB host/slave connection is not so simple.
Although RS232/MIDI may not be the latest, most popular connection
technology, often the simpler solution is the best.

Ray Finch
Albuquerque, New Mexico, USA

 [ To paraphrase the old storekeeper, "If the customer wants USB,
 [ we give him USB!"  ;-)  -- Robbie