The nRF24L01 from Nordic Semiconductors is a unique wireless solution for compact, battery operated applications with stringent requirements on battery lifetime and cost.
The transceiver operates in the licence free worldwide 2,4 GHz ISM band and provides a 2 Mbps air data rate.
Provided in a compact 4 x 4 mm QFN package, the nRF24L01 integrates a complete 2,4 GHz RF transceiver, an RF synthesiser, full baseband logic including the unique Enhanced ShockBurst hardware link layer, advanced power management and a high-speed SPI (serial peripheral interface) for the host controller interface. No external loop filters, resonators or VCO varactor diodes are required, only a low cost ±60 ppm 16 MHz crystal, matching circuitry and the antenna.
The nRF24L01 has a unique combination of four features that enable the implementation of ultra-low power wireless connectivity:
* Less than 13 mA active current for TX and RX, permitting coin-cell battery operation.
* Advanced power management with power-saving idle mode plus rapid active mode startup.
* A high 2 Mbps air data rate that minimises the amount of time the transceiver has to spend in the relatively more power consuming active on-air mode in order to achieve a given effective data rate.
* An Enhanced ShockBurst link layer that minimises processing load on the host microcontroller, reducing average current consumption.
The link layer features both automatic packet handling and automatic packet transaction handling. Automatic packet handling key features include packet assembly, packet detection and validation, dynamic payload length and MultiCeiver support for up to six bidirectional logical links for 1:6 star network topologies. Automatic packet transaction handling key features include acknowledgement of received packages, payload in acknowledegment packet and retransmission of lost packages.
Main benefits of the device include the ability to implement robust, high performance bi-directional and unidirectional data links. On-chip hardware implementation maximises data throughput while minimising on-air time, saving power and improving co-existence performance. Relaxed requirements on the host controller enable a lower cost total solution and a lower processing load for the host controller saves power consumption for the total solution.
Prime applications include wireless mouse, keyboards and joysticks, wireless headsets, intelligent sports equipment (eg, wrist watches and associated sensors), remote control devices and personal area networks (PANs).
Nordic Semiconductor recently unveiled three previously hidden features in the Enhanced ShockBurst hardware link layer. These new features enable significant improvements of power efficiency for bidirectional and unidirectional systems, without adding complexity on the host controller side. These hidden features are Auto Acknowledgement with Payload, Dynamic Payload Length and Selective Auto Acknowledgement.
The features have been included and tested in the nRF24L01 from its original release, but have been previously undocumented. As such there have been no changes to the product, all nRF24L01 transceivers shipped to date have these features. Updated product specification and FAQ web pages are available, providing detailed descriptions of the features and how to use them.
Auto acknowledgement with payload
This feature enables implementation of an efficient bidirectional two-way data link with minimum loading on the host microcontroller. This feature now makes it possible to include a payload in the automatic acknowledgement packet from the primary receiver (PRX) to the primary transmitter (PTX). The host controller simply clocks the payload data into the PRX TX FIFO and the radio will complete the data transmission without further involvement from the host controller.
For a bi-directional data link the main advantages of this feature are lower average power consumption due to less active time for the host controller, plus a faster radio turnaround time and reduced receive cycle. It also enables implementation of advanced power-efficient bidirectional protocols on low-cost host controllers as the radio itself handles all the time-critical processing. Minimising time on air with faster radio turnaround and shorter receive cycles also reduces the probability of packet collisions, thus improving the overall co-existence performance of the system.
Dynamic payload length
This feature enables a more flexible and power-efficient system implementation by offering a dynamic payload length. Instead of having a fixed packet length, each individual packet can have a different length, with a payload size ranging from 1 to 32 bytes. The Enhanced ShockBurst base-band engine will include and decode the payload length info in the packet.
With this feature, therefore, the packet length does not have to be scaled for the largest payload. Instead, each individual packet length is scaled to the size of the actual payload at that time. For applications where there are a variety of payload lengths this can provide significant power savings by minimising on-air time. Always using the shortest packet size necessary reduces the probability of packet collisions, thus improving overall co-existence performance of the system.
Selective auto acknowledgement
When using the auto-acknowledgement feature, designers can select, on a per-packet-basis, whether the PRX primary receiver shall provide an acknowledgement or not. The advantage of this is to again reduce on-air time, thus power consumption, for applications where a subset of the packet transactions does not require guaranteed delivery.
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