CC2500_11 Datasheet, PDF (41/96 Pages) Texas Instruments – Low-Cost Low-Power 2.4 GHz RF Transceiver

CC2500
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 automatically
 Calibrate every fourth time when going
from either RX or TX to IDLE automatically
If the radio goes from TX or RX to IDLE by
issuing an SIDLE strobe, calibration will not be
performed. 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-CCA 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 37 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 SLEEP and listen for incoming
packets without MCU interaction.
When the SWOR strobe command is sent on
the SPI interface, the CC2500 will go to the
SLEEP state when CSn is released. 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.
Set the CC2500 into the IDLE state to exit
WOR mode.
CC2500 can be set up to signal the MCU that a
packet has been received by using the GDO
pins. If a packet is received, the
MCSM1.RXOFF_MODE will determine the
behaviour at the end of the received packet.
When the MCU has read the packet, it can put
the chip back into SLEEP with the SWOR strobe
from the IDLE state. The FIFO will lose its
contents in the SLEEP state.
The WOR timer has two events, Event 0 and
Event 1. In the SLEEP state with WOR
activated, reaching Event 0 will turn on the
digital regulator and start the crystal oscillator.
SWRS040C
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