CC1101
SWRS061H Page 53 of 98
19.5 Wake On Radio (WOR)
The optional Wake on Radio (WOR)
functionality enables
CC1101
to periodically
wake up from SLEEP and listen for incoming
packets without MCU interaction.
When the SWOR strobe command is sent on
the SPI interface, the
CC1101
will go to the
SLEEP state when CSn is released. The RC
oscillator must be enabled before the SWOR
strobe can be used, as it is the clock source
for the WOR timer. The on-chip timer will set
CC1101
into IDLE state and then RX state. After
a programmable time in RX, the chip will go
back to the SLEEP state, unless a packet is
received. See Figure 28 and Section 19.7 for
details on how the timeout works.
To exit WOR mode, set the
CC1101
into the
IDLE state
CC1101
can be set up to signal the MCU that a
packet has been received by using the GDO
pins. If a packet is 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 WOR timer has two events, Event 0 and
Event 1. In the SLEEP state with WOR
activated, reaching Event 0 will turn on 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 an exponent value set by
WORCTRL.WOR_RES. The equation is:
RESWOR
XOSC
Event
EVENT
f
t
_5
0
20
750
The Event 1 timeout is programmed with
WORCTRL.EVENT1. Figure 28 shows the
timing relationship between Event 0 timeout
and Event 1 timeout.
t
Event0
t
Event1
Event1Event0 Event1 Event0
t
Event1
t
Event0
t
State: IDLESLEEP RX SLEEP IDLE
RX
Rx timeout
t
SLEEP
Figure 28: Event 0 and Event 1 Relationship
The time from the
CC1101
enters SLEEP state
until the next Event0 is programmed to
appear, t
SLEEP
in Figure 28, 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 t
SLEEP
is less than 11.08 (10.67) ms, there is
a chance that the consecutive Event 0 will
occur
seconds
too early. Application Note AN047 [4] 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 are 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.
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 to reduce the
current consumption. This is done by setting
WORCTRL.RC_CAL=0 and requires that RC
oscillator calibration values are read from
registers RCCTRL0_STATUS and
RCCTRL1_STATUS and written back to
Note: The FIFO looses its content in the
SLEEP state.
To Next Page
Loading...
Need help?
General
