TRF6900
SINGLE-CHIP RF TRANSCEIVER
SLAS213C – SEPTEMBER 1999 – REVISED MAY 2000
PRINCIPLES OF OPERATION
serial control interface
A 3-wire unidirectional serial bus (CLOCK, DATA, STROBE) is used to program the TRF6900 (see Figure 23).
The internal registers contain all user programmable variables including the DDS frequency setting registers
as well as all control registers.
AteachrisingedgeoftheCLOCKsignal, thelogicvalueontheDATAterminaliswrittenintoa24-bitshiftregister.
Setting the STROBE terminal high loads the programmed information into the selected latch. While the
STROBEsignal is high, the DATA and CLOCK lines must be low (see Figure 2). Since the CLOCK and STROBE
signals are asynchronous, care should be taken to ensure these signals remain free of glitches and noise.
As additional leading bits are ignored, only the least significant 24 bits are serial-clocked into the shift register.
Due to the static CMOS design, the serial interface consumes virtually no current and it can be programmed
in active as well as in standby mode.
Serial Interface
Logic
CLOCK
STROBE
Shift Register
DATA
22
22
A - Latch
B - Latch
3
ADDR
Decoder
ADDR
22
21
C - Latch
D - Latch
Figure 23. Serial Interface Block Diagram
The control words are 24 bits in length. The first incoming bit functions as the most significant bit ( MSB ).
To fully program the TRF6900, four 24-bit words must be sent: the A-, B-, C-, and D-word. If individual bits within
a word are to be changed, then it is sufficient to program only the appropriate 24-bit word.
The definition of the control words are illustrated in Figure 24. Tables 1, 2, and 3 describe the function of each
parameter.
An ADDR equal to 111 is reserved for test purposes and should not be used.
22
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