CC2510F16 Datasheet, PDF (123/244 Pages) Texas Instruments – Low-Power SoC (System-on-Chip) with MCU, Memory, 2.4 GHz RF Transceiver, and USB Controller

12.8 Sleep Timer
The Sleep Timer is used to control when the
CC2510Fx/CC2511Fx exits from PM{0 - 2} and
hence the Sleep Timer can be used to
implement a wake up functionality which
enables CC2510Fx/CC2511Fx to periodically wake
up to active mode and listen for incoming RF
packets.
Note: The Sleep timer should not be used
in active mode
12.8.1 Sleep Timer Operation
This section describes the operation of the
timer.
Note: In this section of the document, f_Ref is
used to denote the reference frequency for
the synthesizer.
For CC2510Fx f_ref = f_XOSC and for
CC2511Fx,
f _ref
=
f _XOSC
2
When referring to the low power RCOSC,
calibrated values are assumed
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 WORCTRL.WOR_RES
register bits. The Sleep Timer is either clocked
by the 32.768 kHz crystal oscillator or by the
low power RC oscillator (f_ref / 750). The timer
can only be used in PM0, PM1, and PM2.
The Sleep Timer has a programmable timing
event called Event 0. While in PM0, PM1, or
PM2, reaching Event 0 will make the
CC2510Fx/CC2511Fx enter active mode.
The time between two consecutive Event 0’s
(t_Event0) is programmed with a mantissa value
CC2510Fx / CC2511Fx
given by WOREVT1.EVENT0 and
WOREVT0.EVENT0, and an exponent value set
by WORCTRL.WOR_RES. When using the low
power RC oscillator to clock the Sleep Timer,
t_Event0 is given by:
t _{Event 0}
=
750
f _ref
⋅ EVENT 0 ⋅ 2^{5⋅WOR _ RES}
If the 32.768 kHz crystal oscillator is used to
clock the Sleep Timer, t_Event0 is calculated as
follows:
t _{Event 0}
=
1
32768
⋅
EVENT 0 ⋅ 2^{5⋅WOR _ RES}
The time from the CC2510Fx/CC2511Fx enters
PM2 until the next Event 0 is programmed to
appear (t_SLEEPmin) should be larger than 11.08
ms when f_ref is 26 MHz and 12 ms when f_ref is
24 MHz (Sleep Timer clocked by the low
power RC oscillator).
t _SLEEPmin
=
750 _{⋅ 384}
f _ref
When the Sleep Timer is clocked by the
32.768 kHz crystal oscillator, t_SLEEPmin = 11.72
ms (384/32768).
12.8.2 Sleep Timer and Power Modes
Entering PM{0 - 2} and/or updating EVENT0
and has to be aligned to a positive edge on the
32 kHz clock source. The following code
examples should be used in order to update
EVENT0 and/or entering PM{0 - 2} correctly:
Please note that the update rate of the
WORTIME0 register will depend on the Sleep
Timer resolution, configured through
WORCTRL.WOR_RES.
// Alignment of entering PM{0 – 2} to a positive edge on the 32 kHz clock source
char temp = WORTIME0;
while(temp == WORTIME0);
// Wait until a positive 32 kHz edge
PCON |= 0x01;
// Enter PM{0 – 2}
// Alignment of updating EVENT0 to a positive edge on the 32 kHz clock source
char temp = WORTIME0;
while(temp == WORTIME0);
// Wait until a positive 32 kHz edge
WOREVT1 = desired event0 >> 8;
// Set EVENT0, high byte
WOREVT0 = desired event0;
// Set EVENT0, low byte
// Alignment of both updating EVENT0 and entering PM{0 - 2}to a positive edge
// on the 32 kHz clock source
char temp = WORTIME0;
while(temp == WORTIME0);
// Wait until a positive 32 kHz edge
WOREVT1 = desired event0 >> 8;
// Set EVENT0, high byte
WOREVT0 = desired event0;
// Set EVENT0, low byte
PCON |= 0x01;
// Enter PM{0 – 2}
SWRS055F
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