14.3.6.5 Measurement Time

The response time of a manually initiated CCA measurement depends on the receiver state.

In RX_ON state, the CCA measurement is done over eight symbol periods and the result is accessible upon the event IRQ_4 (CCA_ED_DONE) or upon CCA_DONE = 1 in the TRX_STATUS register.

In BUSY_RX state, the CCA measurement duration depends on the CCA mode and the CCA request relative to the detection of the SHR. The end of the CCA measurement is indicated by IRQ_4 (CCA_ED_DONE). The variation of a CCA measurement period in BUSY_RX state is described in the table below.

It is recommended to perform CCA measurements in RX_ON state only. To avoid switching accidentally to BUSY_RX state, the SHR detection can be disabled by setting the RX_PDT_DIS bit in the RX_SYN register (RX_SYN.RX_PDT_DIS). The receiver remains in RX_ON state to perform a CCA measurement until the register bit RX_PDT_DIS is set back to continue the frame reception. In this case, the CCA measurement duration is eight symbol periods.

Table 14-29. CCA Measurement Period and Access in BUSY_RX State
CCA Mode	Request within ED measurement⁽¹⁾	Request after ED measurement
1	Energy above threshold.
1	CCA result is available after finishing automated ED measurement period.	CCA result is immediately available after request.
2	Carrier sense only.
2	CCA result is immediately available after request.
3	Carrier sense with Energy above threshold (AND).
3	CCA result is available after finishing automated ED measurement period.	CCA result is immediately available after request.
0	Carrier sense with Energy above threshold (OR).
0	CCA result is available after finishing automated ED measurement period.	CCA result is immediately available after request.

After detecting the SHR, an automated ED measurement is started with a length of eight symbol periods (two symbol periods for high rate PHY modes). This automated ED measurement must be finished to provide a result for the CCA measurement. Only one automated ED measurement per frame is performed.