CC2500-RTR1 datasheet(38/84 Pages) TI

38 / 84 page

CC2500

PRELIMINARY Data Sheet (Rev.1.2)

SWRS040A

Page 38 of 83

CC2500 can be set up to signal the MCU that a

packet has been received by using the GDO

pins.

packet

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

exponent

value

set

WORCTRL.WOR_RES

. The equation is:

RES

WOR

XOSC

Event

EVENT

750

⋅

The Event 1 timeout is programmed with

WORCTRL.EVENT1

. Figure 18 shows the

timing relationship between Event 0 timeout

and Event 1 timeout.

Event0

Event1

Event0

Event1

Event0

Event1

Event0

State:

IDLE

SLEEP

IDLE

Rx timeout

Figure 18: Event 0 and Event 1 relationship

Refer

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

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

XOSC

periods

26 MHz

crystal

IDLE to RX, no calibration

2298

88.4 µs

IDLE to RX, with calibration

~21037

809 µs

IDLE to TX/FSTXON, no calibration

2298

88.4 µs

IDLE to TX/FSTXON, with calibration

~21037

809 µs

TX to RX switch

560

21.5 µs

RX to TX switch

250

9.6 µs

RX or TX to IDLE, no calibration

0.1 µs

RX or TX to IDLE, with calibration

~18739

721 µs

Manual calibration

~18739

721 µs

Table 28: State transition timing

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.

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