Jim - Philips Semi has/had a "brushless dc motor drive circuit", the TDA5140A. It is a sensorless type that connects 3 comparators to the motor's coils, which makes it interesting. Not a text book but the data sheet should provide some insight.
Hul
Jim Thomps> Tim,
AFAIK that's a fairly common way of doing it in software on a motor with trapezoidal back-emf. There's always one terminal that's betwixt and between -- you just drive the other two, and let that one terminal float. The timing of when it gets halfway between the other two voltages tells you where the motor is.
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