CC2500-RTR1 datasheet(37/84 Pages) TI

37 / 84 page

CC2500

PRELIMINARY Data Sheet (Rev.1.2)

SWRS040A

Page 37 of 83

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

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.

CC2500-RTR1 数据表(PDF) 37 Page - Texas Instruments

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