NRF52820-QDAA-R datasheet(171/437 Pages) NORDIC

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Peripherals

6.12.11 Bit counter

The RADIO implements a simple counter that can be configured to generate an event after a specific

number of bits have been transmitted or received.

By using shortcuts, this counter can be started from different events generated by the RADIO and count

relative to these.

The bit counter is started by triggering the BCSTART task, and stopped by triggering the BCSTOP task. A

BCMATCH event will be generated when the bit counter has counted the number of bits specified in the

BCC register. The bit counter will continue to count bits until the DISABLED event is generated or until

the BCSTOP task is triggered. After a BCMATCH event, the CPU can reconfigure the BCC value for new

BCMATCH events within the same packet.

The bit counter can only be started after the RADIO has received the ADDRESS event.

The bit counter will stop and reset on either the BCSTOP, STOP, or DISABLE task, or the END event.

The following figure shows how the bit counter can be used to generate a BCMATCH event in the

beginning of the packet payload, and again generate a second BCMATCH event after sending 2 bytes (16

bits) of the payload.

S0 L S1

PAYLOAD

CRC

RXRU

RXDISABLE

Assuming that the

combined length

of S0, length (L)

and S1 is 12bits.

’X’

Figure 60: Bit counter example

6.12.12 Direction finding

The RADIO implements the Angle-of-Arrival (AoA) and Angle-of-Departure (AoD) Bluetooth Low Energy

feature, which can be used to determine the direction of a peer device. The feature is available for the BLE

1 Mbps and BLE 2 Mbps modes.

When using this feature, the transmitter sends a packet with a continuous tone extension (CTE) appended

to the packet, after the CRC. During the CTE, the receiver can take IQ samples of the incoming signal.

An antenna array is employed at the transmitter (AoD) or at the receiver (AoA). The AoD transmitter, or

AoA receiver, switches between the antennas, in order to collect IQ samples from the different antenna

pairs. The IQ samples can be used to calculate the relative path lengths between the antenna pairs, which

can be used to estimate the direction of the transmitter.

6.12.12.1 CTE format

The CTE is from 16 µs to 160 µs and consists of an unwhitened sequence of 1's, equivalent to a continuous

tone nominally offset from the carrier by +250 kHz for the 1 Mbps PHY and +500 kHz for the 2 Mbps BLE

PHYs. The format of the CTE, when switching and/or sampling, is shown in the following figure.

4463_156 v1.0

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NRF52820-QDAA-R Datasheet(PDF) 171 Page - Nordic Semiconductor

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