CC2500-RTY1 datasheet(42/96 Pages) TI

42 / 96 page

CC2500

SWRS040C

Page 42 of 89

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

shows

the

timing relationship between Event 0 timeout

and Event 1 timeout.

Figure 18: Event 0 and Event 1 Relationship

The time from the

CC2500 enters SLEEP state

until the next Event 0 is programmed to

appear (tSLEEP in Figure 18) should be larger

than 11.08 ms when using a 26 MHz crystal

and 10.67 ms when a 27 MHz crystal is used.

If tSLEEP is less than 11.08 (10.67) ms there is a

chance that the consecutive Event 0 will occur

128

750 

XOSC

seconds

too early. Application Note AN047 [3] explains

in detail the theory of operation and the

different registers involved when using WOR,

as well as highlighting important aspects when

using WOR mode.

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

locked

the

main

crystal

frequency divided by 750.

In applications where the radio wakes up very

often, typically several times every second, it

is possible to do the RC oscillator calibration

once

and

then

turn

off

calibration

(WORCTRL.RC_CAL=0) to reduce the current

consumption. This requires that RC oscillator

calibration values are read from registers

RCCTRL0_STATUS

and

RCCTRL1_STATUS

and written back to RCCTRL0 and RCCTRL0

respectively. If the RC oscillator calibration is

turned off it will have to be manually turned on

again

temperature

and

supply voltage

changes.

Refer to Application Note AN047 [3] for further

details.

19.6

Timing

The radio controller controls most timing in

CC2500, such as synthesizer calibration, PLL

lock time and RX/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 31.2.

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

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