CC2400 Datasheet, PDF (34/84 Pages) Texas Instruments – 2.4 GHz Low-Power RF Transceiver

CC2400
25 Radio control state machine
CC2400 has a built-in state machine that is
used to switch between different operation
states (modes). The change of state is
done either by writing to command strobe
registers, or using dedicated pins.
Before using the radio in either RX or TX
mode, the main crystal oscillator must be
turned on and become stable. The crystal
oscillator has a start-up time given in
Table 8, during which its output is gated
internally to avoid timing problems
stemming from too narrow clock pulses.
The crystal oscillator is controlled by
accessing the SXOSCON/SXOSCOFF
command strobe registers. The
XOSC16M_STABLE bit in the status
register returned during address transfer
indicates whether the oscillator is running
and stable or not (See Table 13). This
status register can be polled when waiting
for the oscillator to start.
The frequency synthesizer (FS) can be
started by either accessing the command
strobe register SFSON or by using the RX
and TX control pins. The FS will then enter
its self-calibration mode. After the
calibration is performed, the FS needs to
lock onto the right LO frequency. The
calibration and lock acquisition time is
given in Table 8.
When the FS is in lock it is possible to go
into RX or TX mode. That can be done
either by accessing the SRX/STX
command strobe registers, or by using the
RX and TX control pins. It is possible to
change quickly between TX and RX by
way of the FS On state.
Turning off RF can be accomplished by
either accessing the command strobe
register SRFOFF or by using the RX and
TX control pins. When using the RX and
TX pins to go from the FS On to Radio Off
it is important that TX is set to 0 before RX
is set to 0.
The state transitions using the RX and TX
pins are illustrated in Figure 15.
Note that to switch between RX and TX,
the FSDIV register must be updated. This
is because direct conversion is used in TX
mode, while an IF frequency of 1 MHz is
used in RX mode. Please see page 47 for
more information about frequency
programming.
Also note that the FSDIV register should
only be changed when the radio is in IDLE
mode, otherwise the PLL can go out of
lock.
SWRS042A
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