CC2500 Datasheet, PDF (36/76 Pages) Texas Instruments – Single Chip Low Cost Low Power RF Transceiver

CC2500
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 32 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 get CC2500 back into the
IDLE state when the timer expires. After a
programmable time in RX, the chip goes back
to SLEEP, unless a packet is received. See
Section 19.7 for details on how the timeout
works.
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 the digital
regulator and start the crystal oscillator. Event
1 follows Event 0 after a programmed timeout.
The time between two consecutive Event 0 is
programmed with a mantissa value given by
WOREVT1.EVENT0 and WOREVT0.EVENT0,
and an exponent value set by
WORCTRL.WOR_RES. The equation is:
t _Event0
=
750
f _XOSC
⋅ EVENT 0 ⋅ 2^{5⋅WOR _ RES}
The Event 1 timeout is programmed with
WORCTRL.EVENT1. Figure 13 shows the
timing relationship between Event 0 timeout
and Event 1 timeout.
Rx timeout
State: SLEEP IDLE RX
SLEEP IDLE RX
Event0 Event1
Event0 Event1
t
t_Event0
t_Event0
t_Event1
t_Event1
Figure 13: Event 0 and Event 1 relationship
19.5.1 RC Oscillator and Timing
The frequency of the low-power RC oscillator
used for the WOR functionality varies with
temperature and supply voltage. In order to
Preliminary Data Sheet (rev.1.1.) SWRS040
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