MRF49XAT-I-ST Datasheet, PDF (65/102 Pages) Microchip Technology – ISM Band Sub-GHz RF Transceiver

3.16 Sleep, Wake-up and Battery
Operations
The advanced interrupt handler circuit is configured in
the transmitter to reduce the power consumption. As
mentioned, the Sleep mode is the lowest power
consumption mode in which the clock and all functional
blocks of the device are disabled. In case of any
interrupt, the device wakes up, switches to Active mode
and an interrupt signal generated on the IRO pin
indicates the change in state to the host
microcontroller. The source of the interrupt can be
determined by reading the status word of the device
(see Register 2-1).
To reduce current consumption, the MRF49XA should
be placed in the low-power consuming Sleep mode. In
Sleep mode, the 10 MHz main oscillator is turned off,
disabling the RF and baseband circuitry. Data is
retained in the control and FIFO registers and the
transceiver is accessible through the SPI port.
The MRF49XA will not enter Sleep mode if any of the
interrupt remains active, irrespective of the state of the
OSCEN bit in the PMCREG. This way, the
microcontroller can always have a clock signal to
process the interrupt. To prevent high-current
consumption, which results in shorter battery life, it is
highly recommended to process and clear interrupts
before entering Sleep mode. The functions which are
not necessary should be turned off to avoid unwanted
interrupts.
To minimize the current consumption, the MRF49XA
supports different power-saving modes, along with an
integrated wake-up timer. Active mode can be
reinitiated by the following ways:
• By applying the wake-up events’ negative logical
pulse on INT pin
• Wake-up timer time-out
• Low supply voltage detection
• On-chip FIFO filled up
• On receiving a request through the serial interface
To make the MRF49XA device enter into Sleep mode,
certain control register values must be initialized. The
sequence to program the control registers for entering
into Sleep and Wake-up modes is as follows:
For Sleep mode:
1. Check the IRO bit status
2. Read STSREG
3. Configure GENCREG
4. Configure PMCREG for oscillator and clock
buffering
For Wake-up mode:
1. Enter in TX/RX mode or
2. Enable crystal or
3. Set the INT pin
MRF49XA
The device has the ability to wake itself up from Sleep
mode through a wake-up timer. The WTSREG sets the
wake-up interval for the MRF49XA. After setting the
wake-up interval, the WUTEN bit (PMCREG<1>)
should be cleared and set at the end of every wake-up
cycle.
The Wake-up Duration Time (WUTIME) is calculated
as shown in Equation 3-4.
EQUATION 3-4:
WUTIME = 1.03 x WTMV<7:0> x 2^WTEV<4:0> + 0.5 ms
where:
WTMV<7:0> = Decimal Value between 0 to 255
WTEV<4:0> = Decimal Value between 0 to 29
Note: WUTIME is measured in ms.
The Battery Threshold Detect feature is useful in
monitoring the discharge-sensitive batteries, such as
Lithium cells. The LBDEN bit (PMCREG<2>) is used to
enable or disable the low battery detect feature.
The BCSREG configures the following:
• Output clock frequency
• Low battery detect threshold
The low battery threshold value is programmable from
2.2V to 3.8V and is calculated by using Equation 3-5.
EQUATION 3-5:
Threshold Voltage Value = 2.25 + 0.1 x (LBDVB<3:0>)
where:
LBDVB<3:0> is the Decimal Value from 0-15
When the battery level falls 50 mV below this value, the
LBTD bit (STSREG<10>) is set, indicating that the
battery level is below the programmed threshold.
The registers associated with power-saving modes
are:
• STSREG (see Register 2-1)
• GENCREG (see Register 2-2)
• TXCREG (see Register 2-4)
• RXCREG (see Register 2-7)
• PMCREG (see Register 2-13)
• WTSREG (see Register 2-14)
• BCSREG (see Register 2-16)
© 2009-2011 Microchip Technology Inc.
Preliminary
DS70590C-page 65