14.3.5.2 Measurement Description

There are two ways to initiate an ED measurement,

• Manually by writing an arbitrary value to the PHY_ED_LEVEL register, or
• Automatically after detection of a valid SHR of an incoming frame.

Manually:

For manually initiated ED measurements, the radio transceiver needs to be either in the state RX_ON or BUSY_RX. The end of the ED measurement time (eight symbol periods plus a processing time) is indicated by the interrupt IRQ_4 (CCA_ED_DONE) and the measurement result is stored in register PHY_ED_LEVEL register, refer to t_ED in the Block Initialization and Settling Time table.

In order to avoid interference with an automatically initiated ED measurement, the SHR detection can be disabled by setting the RX_PDT_DIS bit in the RX_SYN register (RX_SYN.RX_PDT_DIS).

Automatically:

An automated ED measurement is started upon SHR detection. The end of the automated measurement is not signaled by an interrupt.

When using the Basic Operating Mode and standard compliant data rates, a valid ED value (PHY_ED_LEVEL register) of the currently received frame is accessible not later than eight symbol periods after IRQ_2 (RX_START) plus a processing time of 12µs. For High Data Rate Modes, the measurement duration is reduced to two symbol periods plus a processing time of 12µs. The ED value remains valid until a new RX_START interrupt is generated by the next incoming frame or until another ED measurement is initiated.

When using the Extended Operating Mode, it is useful to mask IRQ_2 (RX_START), thus the interrupt cannot be used as timing reference. A successful frame reception is signalized by interrupt IRQ_3 (TRX_END). In this case, the ED value needs to be read within the time span of a next SHR detection plus the ED measurement time in order to avoid overwrite of the current ED value.