14.2.1.2.1 P_ON – Power-On after V_DD

When the external supply voltage (V_DD) is applied first to the AT86RF212B, the radio transceiver goes into P_ON state performing an on-chip reset. The crystal oscillator is activated and the default 1MHz master clock is provided at pin 17 (CLKM) after the crystal oscillator has stabilized. CLKM can be used as a clock source to the microcontroller. The SPI interface and digital voltage regulator (DVREG) are enabled.

The on-chip power-on-reset sets all registers to their default values. A dedicated reset signal from the microcontroller at pin 8 (/RST) is not necessary, but recommended for hardware / software synchronization reasons.

All digital inputs are pulled-up or pulled-down during P_ON state. This is necessary to support microcontrollers where GPIO signals are floating after power-on or reset. The input pull-up and pull-down transistors are disabled when the radio transceiver leaves P_ON state towards TRX_OFF state. A reset during P_ON state does not change the pull-up and pull-down configuration.

Leaving P_ON state, output pins DIG1/DIG2 are pulled-down to digital ground, whereas pins DIG3/DIG4 are pulled-down to analog ground, unless their configuration is changed.

Prior to leaving P_ON, the microcontroller must set the AT86RF212B pins to the default operating values: pin 11 (SLP_TR) = L, pin 8 (/RST) = H and pin 23 (/SEL) = H.

All interrupts are disabled by default. Thus, interrupts for state transition control are to be enabled first, for example enable IRQ_4 (AWAKE_END) to indicate a state transition to TRX_OFF state or interrupt IRQ_0 (PLL_LOCK) to signal a locked PLL in PLL_ON state. In P_ON state a first access to the radio transceiver registers is possible after a default 1MHz master clock is provided at pin 17 (CLKM), refer to t_TR1 in the State Transition Timing Summary.

Once the supply voltage has stabilized and the crystal oscillator has settled (see parameter t_XTAL refer to Table 7-2), the interrupt mask for the AWAKE_END should be set. A valid SPI write access to TRX_CMD bits in the TRX_STATE register (TRX_STATE.TRC_CMD) with the command TRX_OFF or FORCE_TRX_OFF initiate a state change from P_ON towards TRX_OFF state, which is then indicated by an interrupt IRQ_4 (AWAKE_END) if enabled.