Rf12 – Rainbow Electronics RF12 User Manual

Page 20

RF12

Note:

Lock bit is high when the AFC loop is locked, f same bit indicates when two subsequent measuring

results are the same, toggle bit changes state in every measurement cycle.

In automatic operation mode (no strobe signal is needed from the microcontroller to update the

output offset register) the AFC circuit is automatically enabled when the VDI indicates potential incoming

signal during the whole measurement cycle and the circuit measures the same result in two subsequent

cycles.

There are three operation modes, example from the possible application:

, (a1=0, a0=1) The circuit measures the frequency offset only once after power up. In this way

extended TX-RX maximum distance can be achieved.

Possible application:

In the final application, when the user inserts the battery, the circuit measures and compensates for

the frequency offset caused by the crystal tolerances. This method allows for the use of a cheaper quartz

in the application and provides protection against tracking an interferer.

, (a1=1, a0=0) The circuit automatically measures the frequency offset during an initial effective

low data rate pattern –easier to receive (i.e.: 00110011) of the package and changes the receiving

frequency accordingly. The further part of the package can be received by the corrected frequency

settings.

, (a1=1, a0=0) The transmitter must transmit the first part of the packet with a step higher

deviation and later there is a possibility to reduce it.

In both cases (2a and 2b), when the VDI indicates poor receiving conditions (VDI goes low), the

output register is automatically cleared. Use these settings when receiving signals from different

transmitters transmitting in the same nominal frequencies.

, (a1=1, a0=1) It’s the same as 2a and 2b modes, but suggested to use when a receiver operates

with only one transmitter. After a complete measuring cycle, the measured value is kept independently of

the state of the VDI signal.

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