What's the deal with the "CPU board" exemption?
"CPU board. A circuit board that contains a microprocessor, or frequency determining circuitry for the microprocessor, the primary function of which is to execute user-provided programming, but not including: A circuit board that contains only a microprocessor intended to operate under the primary control or instruction of a microprocessor external to such a circuit board; or A circuit board that is a dedicated controller for a storage or input/output device."
So if one sells a board that has say a PIC on it and some support logic, and the 9kHz+ signals are all internal to the uP (self-clock), but it's otherwise a functionally complete design other than it's not in a housing, is that an exempt product?