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Revision 3.6

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AS3977

Data Sheet - A p p l i c a t i o n I n f o r m a t i o n

Figure 6. Operation Mode Relations

9.2 Transmitter Control Interface

The AS3977 is controlled by an external micro controller (µC) via. a bi-directional communication interface (serial digital interface, SDI). The SDI

enables data to be read from and written to internal control registers without the necessity of an internal clock signal. Analog de-bouncing of

clock and data input is implemented in order to improve the overall system reliability.

The SDI-control interface includes a state machine, which expects a command control word as first byte and in reference to this byte, the

interface is configured as write, read, or transmit operation. This method enables an effective and easy control of basic transmitter functions.

Four preset independent output frequencies and two preset independent output power levels and modulation types can be selected using the

control-command byte, thus enabling fast channel hopping and/or fast changes to the output power level and modulation type. The selection of

the active output frequency and/or power level and modulation type is done using the so-called command byte.

As an additional feature, the AS3977 provides a configurable clock signal derived from the crystal frequency. The purpose of this clock signal is

to provide a µC clock and to enable data synchronization.

A timer is included to power down (Power Down Mode) the transmitter after a certain time, which is defined as 2

oscillator- Period.

Transmit Mode

PLL Enable

Mode

Clock Enable

Mode

Power Down

Mode

External

Hardware

Reset

Power ON

ENABLE High

Pulse

ENABLE is

HIGH

SPI

Command

SPI

Command

ENABLE to LOW for 2

16

XTAL cycles

or

Software Power Down

command via SPI