CC2510FX Datasheet, PDF (113/253 Pages) List of Unclassifed Manufacturers – True System-on-Chip with Low Power RF Transceiver and 8051 MCU

CC2510Fx / CC2511Fx
13.5 Sleep Timer
The Sleep Timer is used to control when
the CC2510Fx/CC2511Fx exits from the low-
power modes PM1 or PM2. Thus the
Sleep Timer can be used to implement a
wake up functionality which enables
CC2510Fx/CC2511Fx 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 either clocked by the 32.768 kHz
crystal oscillator or the 34.6667 kHz
(26MHz / 750) low power RC oscillator.
The timer runs in all power modes except
PM3 where all oscillators are powered off.
The timer can be reset by writing 1 to the
WORCTL.WOR_RESET register bit.
The Sleep Timer has a programmable
timing event called Event 0. While in
power mode PM1 or PM2, reaching Event
0 will turn on the digital voltage regulator
and start the crystal oscillator.
The time between two consecutive Event
0’s is programmed with timeout value set
by a mantissa value given by
WOREVT1.EVENT0
and
WOREVT0.EVENT0, and an exponent
value set by WORCTRL.WOR_RES. The
equation is:
t _{Event 0}
=
750
f _XOSC
⋅ EVENT 0 ⋅ 2^{5⋅WOR _ RES}
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 RC oscillator will be
calibrated whenever possible, which is
when the 26/48 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 26/48 MHz crystal oscillator
frequency divided by 750. To generate a
32.768 kHz RC oscillator frequency, use a
24.576 MHz crystal for the 26 MHz crystal
oscillator.
13.5.3 Sleep Timer Interrupt
The Sleep Timer generates the Sleep
Timer interrupt, ST, when the timing event
Event 0 occurs. This interrupt source can
be
masked
using
the
WORIRQ.EVENT0_MASK interrupt mask
bit. The interrupt flag bit
WORIRQ.EVENT0_FLAG will be set when
Event 0 occurs.
13.5.4 Sleep Timer Registers
The SFR registers associated with the
Sleep Timer are described in the following
CC2510Fx/CC2511Fx PRELIMINARY Data Sheet (Rev. 1.2) SWRS055A Page 113 of
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