User Manual

Revision 1.0 Page 23 of 78
nRF24L01+ Product Specification
6.1.3.2 Standby-II mode
In standby-II mode extra clock buffers are active and more current is used compared to standby-I mode.
nRF24L01+ enters standby-II mode if CE is held high on a PTX device with an empty TX FIFO. If a new
packet is uploaded to the TX FIFO, the PLL immediately starts and the packet is transmitted after the nor-
mal PLL settling delay (130µs).
Register values are maintained and the SPI can be activated during both standby modes. For start up
times see Table 16. on page 24
.
6.1.4 RX mode
The RX mode is an active mode where the nRF24L01+ radio is used as a receiver. To enter this mode, the
nRF24L01+ must have the PWR_UP bit, PRIM_RX bit and the CE pin set high.
In RX mode the receiver demodulates the signals from the RF channel, constantly presenting the demodu-
lated data to the baseband protocol engine. The baseband protocol engine constantly searches for a valid
packet. If a valid packet is found (by a matching address and a valid CRC) the payload of the packet is pre-
sented in a vacant slot in the RX FIFOs. If the RX FIFOs are full, the received packet is discarded.
The nRF24L01+ remains in RX mode until the MCU configures it to standby-I mode or power down mode.
However, if the automatic protocol features (Enhanced ShockBurst™) in the baseband protocol engine are
enabled, the nRF24L01+ can enter other modes in order to execute the protocol.
In RX mode a Received Power Detector (RPD) signal is available. The RPD is a signal that is set high
when a RF signal higher than -64 dBm is detected inside the receiving frequency channel. The internal
RPD signal is filtered before presented to the RPD register. The RF signal must be present for at least 40µs
before the RPD is set high. How to use the RPD is described in Section 6.4 on page 25
.
6.1.5 TX mode
The TX mode is an active mode for transmitting packets. To enter this mode, the nRF24L01+ must have
the PWR_UP bit set high, PRIM_RX bit set low, a payload in the TX FIFO and a high pulse on the CE for
more than 10µs.
The nRF24L01+ stays in TX mode until it finishes transmitting a packet. If CE = 0, nRF24L01+ returns to
standby-I mode. If CE = 1, the status of the TX FIFO determines the next action. If the TX FIFO is not
empty the nRF24L01+ remains in TX mode and transmits the next packet. If the TX FIFO is empty the
nRF24L01+ goes into standby-II mode. The nRF24L01+ transmitter PLL operates in open loop when in TX
mode. It is important never to keep the nRF24L01+ in TX mode for more than 4ms at a time. If the
Enhanced ShockBurst™ features are enabled, nRF24L01+ is never in TX mode longer than 4ms.