CC2520_11 Datasheet, PDF (88/133 Pages) Texas Instruments – 2.4 GHZ IEEE 802.15.4/ZIGBEE RF TRANSCEIVER

CC2520 DATASHEET
2.4 GHZ IEEE 802.15.4/ZIGBEE® RF TRANSCEIVER
SWRS068 – DECEMBER 2007
23 External Clock Output
CC2520 can provide a 50-50 duty cycle clock signal to external circuits. This is an advantage for low-cost
systems where one wants as few components as possible, because both the microcontroller and CC2520
can run on the same crystal. CC2520 has a clock divider that can make glitch free changes between many
different frequencies between 1 and 16 MHz.
After a reset, CC2520 will output a 1MHz clock on GPIO0. Note that CC2520 needs to be in active mode in
order for the crystal oscillator to be running and thus have the ability to provide an external clock.
The procedure for waking a system up from LPM2 is as follows:
• MCU is running on RC oscillator, CC2520 is in LPM2
• Change CC2520 from LPM2 to active mode.
• Switch the MCU over to the 1 MHz clock that CC2520 outputs on GPIO0.
• Change to the desired clock frequency.
The procedure for bringing a system from active mode to LPM2 is as follows:
• Switch MCU over to RC oscillator.
• Set CC2520 in LPM2.
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