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CC1101pins. If a packet is received, theMCSM1.RXOFF_MODE will determine thebehaviour at the end of the received packet.When the MCU has read the packet, it can putthe chip back into SLEEP with the SWOR strobefrom the IDLE state. The FIFO will loose itscontents in the SLEEP state.The WOR timer has two events, Event 0 andEvent 1. In the SLEEP state with WORactivated, reaching Event 0 will turn on thedigital regulator and start the crystal oscillator.Event 1 follows Event 0 after a programmedtimeout.The time between two consecutive Event 0 isprogrammed with a mantissa value given byWOREVT1.EVENT0 and WOREVT0.EVENT0,and an exponent value set byWORCTRL.WOR_RES. The equation is:t750 ⋅5 WOR _ RESEvent0 = ⋅ EVENT 0 ⋅ 2fXOSCThe Event 1 timeout is programmed withWORCTRL.EVENT1. Figure 19 shows thetiming relationship between Event 0 timeoutand Event 1 timeout.as well as highlighting important aspects whenusing WOR mode.19.5.1 RC Oscillator and TimingThe frequency of the low-power RC oscillatorused for the WOR functionality varies withtemperature and supply voltage. In order tokeep the frequency as accurate as possible,the RC oscillator will be calibrated wheneverpossible, which is when the XOSC is runningand the chip is not in the SLEEP state. Whenthe power and XOSC is enabled, the clockused by the WOR timer is a divided XOSCclock. When the chip goes to the sleep state,the RC oscillator will use the last validcalibration result. The frequency of the RCoscillator is locked to the main crystalfrequency divided by 750.In applications where the radio wakes up veryoften, typically several times every second, itis possible to do the RC oscillator calibrationonce and then turn off calibration(WORCTRL.RC_CAL=0) to reduce the currentconsumption. This requires that RC oscillatorcalibration values are read from registersRCCTRL0_STATUS and RCCTRL1_STATUSand written back to RCCTRL0 and RCCTRL1respectively. If the RC oscillator calibration isturned off it will have to be manually turned onagain if temperature and supply voltagechanges.Refer to Application Note AN047 [4] for furtherdetails.Figure 19: Event 0 and Event 1 RelationshipThe time from the CC1101 enters SLEEP stateuntil the next Event0 is programmed to appear(t SLEEP in Figure 19) should be larger than11.08 ms when using a 26 MHz crystal and10.67 ms when a 27 MHz crystal is used. Ift SLEEP is less than 11.08 (10.67) ms there is achance that the consecutive Event 0 will occur750 ⋅128 secondsf XOSCtoo early. Application Note AN047 [4] explainsin detail the theory of operation and thedifferent registers involved when using WOR,19.6 TimingThe radio controller controls most of the timingin CC1101, such as synthesizer calibration, PLLlock time, and RX/TX turnaround times. Timingfrom IDLE to RX and IDLE to TX is constant,dependent on the auto calibration setting.RX/TX and TX/RX turnaround times areconstant. The calibration time is constant18739 clock periods. Table 28 shows timing incrystal clock cycles for key state transitions.Power on time and XOSC start-up times arevariable, but within the limits stated in Table 7.Note that in a frequency hopping spreadspectrum or a multi-channel protocol thecalibration time can be reduced from 721 µs toapproximately 150 µs. This is explained inSection 32.2.SWRS061C Page 45 of 94