5. Radio Initialization
5.1 Radio Chip Wake Up
First, the radio is in the off state. After the SDN pin is pulled low, the radio wakes up and performs a Power on Reset which takes a
maximum of 5 ms until the chip is ready to receive commands on the SPI bus. The GPIO1 pin goes high when the radio is ready for
receiving SPI commands. During the reset period, the radio cannot accept any SPI commands. There are two ways to determine if the
chip is ready to receive SPI commands after a reset event. Either use a timer in the host microcontroller to wait or connect the GPIO1
pin of the radio to the host MCU and poll the status of this pin. During power on reset, it remains low. Once the reset is finished, the
radio sets the GPIO1 to the high state.
Next, the radio device has to be sent to active mode by issuing a POWER_UP command via the SPI interface which takes approxi-
mately 5 ms to be completed. It can be monitored in three ways. If the command is completed either the GPIO1 pin of the radio goes
low by issuing the command and the radio sets it to high state or the NIRQ pin is asserted or the host MCU can monitor CTS over the
SPI.
AN954: Programming Guide for EFM8 and EZRadio ®
Radio Initialization
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