I'll do that.
BTW do you know whether if incoming TX frequency was greater than the LO frequency, would the AfcValue be positive or negative? There's the description about FEI "This function provides information about the frequency error of the local oscillator (LO) compared with the carrier frequency of a modulated signal at the input of the receiver" so I'm reading that as the 'error' is LO - TX (i.e. positive if LO is greater than TX, negative if LO is less than TX), so I assume you have to subtract it from the FRF register value to match the incoming TX frequency.
Mark.
Edit: I've answered my question, it's much clearer in the Freescale AFC app note: "The Frequency Error Indicator block stores the result and that FEI value is used by the AFC block, which then subtracts the value from the RF Carrier Frequency registers, driving the LO to the desired frequency."