CC2500_06 Datasheet, PDF (37/84 Pages) Texas Instruments – Single Chip Low Cost Low Power RF Transceiver

CC2500
If the XOSC is forced on, the crystal will
always stay on even in the SLEEP state.
Crystal oscillator start-up time depends on
crystal ESR and load capacitances. The
electrical specification for the crystal oscillator
can be found in Section 4.4 on page 10.
19.3 Voltage Regulator Control
The voltage regulator to the digital core is
controlled by the radio controller. When the
chip enters the SLEEP state, which is the state
with the lowest current consumption, the
voltage regulator is disabled. This occurs after
CSn is released when a SPWD command
strobe has been sent on the SPI interface. The
chip is now in the SLEEP state. Setting CSn
low again will turn on the regulator and crystal
oscillator and make the chip enter the IDLE
state.
When wake on radio is enabled, the WOR
module will control the voltage regulator as
described in Section 19.5.
19.4 Active Modes
CC2500 has two active modes: receive and
transmit. These modes are activated directly
by the MCU by using the SRX and STX
command strobes, or automatically by Wake
on Radio.
The frequency synthesizer must be calibrated
regularly. CC2500 has one manual calibration
option (using the SCAL strobe), and three
automatic calibration options, controlled by the
MCSM0.FS_AUTOCAL setting:
• Calibrate when going from IDLE to
either RX or TX (or FSTXON)
• Calibrate when going from either RX
or TX to IDLE
• Calibrate every fourth time when going
from either RX or TX to IDLE
The calibration takes a constant number of
XOSC cycles (see Table 28 for timing details).
When RX is activated, the chip will remain in
receive mode until a packet is successfully
received or the RX termination timer expires
(see Section 19.7). Note: the probability that a
false sync word is detected can be reduced by
using PQT, CS, maximum sync word length
and sync word qualifier mode as describe in
Section 17. After a packet is successfully
received the radio controller will then go to the
state indicated by the MCSM1.RXOFF_MODE
setting. The possible destinations are:
• IDLE
• FSTXON: Frequency synthesizer on
and ready at the TX frequency.
Activate TX with STX.
• TX: Start sending preambles
• RX: Start search for a new packet
Similarly, when TX is active the chip will
remain in the TX state until the current packet
has been successfully transmitted. Then the
state will change as indicated by the
MCSM1.TXOFF_MODE setting. The possible
destinations are the same as for RX.
The MCU can manually change the state from
RX to TX and vice versa by using the
command strobes. If the radio controller is
currently in transmit and the SRX strobe is
used, the current transmission will be ended
and the transition to RX will be done.
If the radio controller is in RX when the STX or
SFSTXON command strobes are used, the “TX
if clear channel” function will be used. If the
channel is not clear, the chip will remain in RX.
The MCSM1.CCA_MODE setting controls the
conditions for clear channel assessment. See
Section 17.5 on page 33 for details.
The SIDLE command strobe can always be
used to force the radio controller to go to the
IDLE state.
19.5 Wake On Radio (WOR)
The optional Wake on Radio (WOR)
functionality enables CC2500 to periodically
wake up from deep sleep and listen for
incoming packets without MCU interaction.
When WOR is enabled, the CC2500 will go to
the SLEEP state when CSn is released after
the SWOR command strobe has been sent on
the SPI interface. The RC oscillator must be
enabled before the WOR strobe can be used,
as it is the clock source for the WOR timer.
The on-chip timer will set CC2500 into the IDLE
state and then the RX state. After a
programmable time in RX, the chip goes back
to the SLEEP state, unless a packet is
received. See Figure 18 and Section 19.7 for
details on how the timeout works.
PRELIMINARY Data Sheet (Rev.1.2) SWRS040A
Page 37 of 83