CC2500_06 Datasheet, PDF (38/84 Pages) Texas Instruments – Single Chip Low Cost Low Power RF Transceiver

CC2500
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 18 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 18: Event 0 and Event 1 relationship
the power and XOSC is enabled, the clock
used by the WOR timer is a divided XOSC
clock. When the chip goes to the sleep state,
the RC oscillator will use the last valid
calibration result. The frequency of the RC
oscillator is locked to the main crystal
frequency divided by 750.
19.6 Timing
The radio controller controls most timing in
CC2500, such as synthesizer calibration, PLL
lock and RT/TX turnaround times. Timing from
IDLE to RX and IDLE to TX is constant,
dependent on the auto calibration setting.
RX/TX and TX/RX turnaround times are
constant. The calibration time is constant
18739 clock periods. Table 28 shows timing in
crystal clock cycles for key state transitions.
Power on time and XOSC start-up times are
variable, but within the limits stated in Table 7.
Note that in a frequency hopping spread
spectrum or a multi-channel protocol the
calibration time can be reduced from 721 µs to
approximately 150 µs. This is explained in
Section 30.2.
Description
IDLE to RX, no calibration
IDLE to RX, with calibration
IDLE to TX/FSTXON, no calibration
IDLE to TX/FSTXON, with calibration
TX to RX switch
RX to TX switch
RX or TX to IDLE, no calibration
RX or TX to IDLE, with calibration
Manual calibration
XOSC
periods
2298
~21037
2298
~21037
560
250
2
~18739
~18739
26 MHz
crystal
88.4 µs
809 µs
88.4 µs
809 µs
21.5 µs
9.6 µs
0.1 µs
721 µs
721 µs
Table 28: State transition timing
Refer to Application Note AN038
CC1100/CC2500 Wake-on-Radio for further
details.
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
keep the frequency as accurate as possible,
the RC oscillator will be calibrated whenever
possible, which is when the XOSC is running
and the chip is not in the SLEEP state. When
19.7 RX Termination Timer
CC2500 has optional functions for automatic
termination of RX after a programmable time.
The main use for this functionality is wake-on-
radio (WOR), but it may be useful for other
applications. The termination timer starts when
in RX state. The timeout is programmable with
the MCSM2.RX_TIME setting. When the timer
expires, the radio controller will check the
condition for staying in RX; if the condition is
not met, RX will terminate. After the timeout,
the condition will be checked continuously.
PRELIMINARY Data Sheet (Rev.1.2) SWRS040A
Page 38 of 83