Peter,
Unfortunately, I couldn't find any vi's internally or out on the web that are what you are looking for. If you have to build your own vi, there is a lot of information on using the serial port on our website. Also, for more information on Microwire, I would check out www.national.com since it appears National Semiconductor developed this protocol.
Thanks.
Matt Kisler
Applications Engineer
National Instruments
http://www.ni.com/ask