Rainbow Electronics RF22 - Manual (Page 40)

RF22
Version: 0.1 Date: 12/23/2008
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Use of the D variable in the formula is only necessary if finer resolution is required than the R value gives.
Add R/W Function/Description D7 D6 D5 D4 D3 D2 D1 D0 POR Def.
14 R/W Wake-Up Timer Period 1 wtr[3] wtr[2] wtr[1] wtr[0] wtd[1] wtd[0] 00h
15 R/W Wake-Up Timer Period 2 wtm[15] wtm[14] wtm[13] wtm[12] wtm[11] wtm[10] wtm[9] wtm[8] 00h
16 R/W Wake-Up Timer Period 3 wtm[7] wtm[6] wtm[5] wtm[4] wtm[3] wtm[2] wtm[1] wtm[0] 00h
17 R Wake-Up Timer Value 1 wtv[15] wtv[14] wtv[13] wtv[12] wtv[11] wtv[10] wtv[9] wtv[8] —
18 R Wake-Up Timer Value 2 wtv[7] wtv[6] wtv[5] wtv[4] wtv[3] wtv[2] wtv[1] wtv[0] —
There are two different methods for utilizing the wake-up timer (WUT) depending on if the WUT interrupt is enabled in
"Register 06h. Interrupt Enable 2". If the WUT interrupt is enabled then nIRQ pin will go low when the timer expires.
The chip will also change state so that the 30M XTAL is enabled so that the microcontroller clock output is available for
the microcontroller to use process the interrupt. The other method of use is to not enable the WUT interrupt and use
the WUT GPIO setting. In this mode of operation the chip will not change state until commanded by the microcontroller.
The two different modes of operation of the WUT are demonstrated in Figure 27.
A 32 kHz XTAL may also be used for better timing accuracy. By setting the x32ksel bit in 07h, GPIO0 is automatically
reconfigured so that an external 32 kHz XTAL may be connected to this pin. In this mode, the GPIO0 is extremely
sensitive to parasitic capacitance, so only the XTAL should be connected to this pin and the XTAL should be physically
located as close to the pin as possible. Once the x32ksel bit is set, all internal functions such as WUT, micro-controller
clock, and LDC mode will use the 32K XTAL and not the 32 kHz RC oscillator.
WUT Period
GPIOX=00001
nIRQ
SPI Interrupt
Read
Chip State
Current
Consumption
Sleep Ready Sleep Ready Sleep Ready Sleep
600n
1mA
600n
1mA
600n
1mA
WUT Period
GPIOX=00001
nIRQ
SPI Interrupt
Read
Chip State
Current
Consumption
Sleep
600n
Interrupt Enable enwut=1 (Reg 06h)
Interrupt Enable enwut=0 (Reg 06h)
Figure27. WUT Interrupt and WUT Operation
8.7. Low Duty Cycle Mode
The Low Duty Cycle Mode is available to automatically wake-up the receiver to check if a valid signal is available. The
basic operation of the low duty cycle mode is demonstrated in the figure below. If a valid preamble or sync word is not
detected the chip will return to sleep mode until the beginning of a new WUT period. If a valid preamble and sync are
detected the receiver on period will be extended for the low duty cycle mode duration (TLDC) to receive all of the
packet. The time of the TLDC is determined by the formula below: