"Erik Malund also gives frequent references here to a number of very good documents from Philips"

They are the three 80C51_FAM_*.pdf documents at:
http://www.semiconductors.philips.com/products/...other.html

"And of course if you do a little searching you'll probably find some source code that will do it all for you."

Keil have an example in their downloads area, and Mark Odell recently posted an example in the Keil discussion forum.