CC1110-RTR1 datasheet(104/203 Pages) TI

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CC1110

CC1110 PRELIMINARY Datasheet (Rev. 1.01) SWRS033A

Page 104 of 202

13.5 Sleep Timer

The Sleep Timer is used to control when

the

CC1110 exits from the low-power modes

PM1 or PM2. Thus the Sleep Timer can be

used to implement a wake up functionality

which enables

CC1110 to periodically wake

up from low-power mode and listen for

incoming RF packets. Additionally the

Sleep Timer can be used as a real time

clock when the 32.768 kHz crystal

oscillator is used.

13.5.1 Sleep Timer Operation

This section describes the operation of the

timer.

The Sleep Timer consists of a 31-bit

counter. The appropriate bits of this

counter are selected according to a

resolution setting determined by the

WORCTL.WOR_RES register bits. The Sleep

Timer is clocked by the 32.768 kHz clock.

The source for this clock is either the

32.768 kHz crystal oscillator or the 34 kHz

low power RC oscillator. The timer runs in

all power modes except PM3 where all

oscillators are powered off. The timer can

reset

writing

the

WORCTL.WOR_RESET register bit.

The Sleep Timer has two programmable

timing events called Event 0 and Event 1.

While in power mode PM1 or PM2,

reaching Event 0 will turn on the digital

voltage regulator and start the crystal

oscillator. Event 1 always follows Event 0

after a programmed timeout.

The time between two consecutive Event

0’s is programmed with timeout value set

mantissa

value

given

WOREVT1.EVENT0

and

WOREVT0.EVENT0,

and

exponent

value set by WORCTRL.WOR_RES. The

equation is:

RES

WOR

XOSC

Event

EVENT

750

⋅

The Event 1 timeout is programmed with

WORCTRL.EVENT1.

Figure 19 shows the timing relationship

between Event 0 timeout and Event 1

timeout.

Event0

Event1

Event0

Event1

Event0

Event1

Event0

Figure 19: Event 0 and Event 1

Relationship

13.5.2 Low power RC oscillator and

timing

This section applies to using the low

power RC oscillator as clock source for the

Sleep Timer.

The frequency of the low-power RC

oscillator, which can be used as clock

source for the Sleep Timer, varies with

temperature and supply voltage. In order

to keep the frequency as accurate as

possible,

the

oscillator

will

calibrated whenever possible, which is

when the 26 MHz crystal oscillator is

running and the chip is in the PM0 power

mode. When the chip goes to PM1 or

PM2, the RC oscillator will use the last

valid calibration result. The frequency of

the low power RC oscillator is therefore

locked to the 26 MHz crystal oscillator

frequency divided by 750.

13.5.3 Sleep Timer Interrupts

The Sleep Timer generates the Sleep

Timer interrupt, ST, when one of the timing

events Event 0 or Event 1, occur. Each of

these interrupt sources can be masked

using the WORIRQ interrupt mask bits. The

interrupt flag bits in WORIRQ will be set

when the corresponding event occurs.

13.5.4 Sleep Timer Registers

The SFR registers associated with the

Sleep Timer are described in the following

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