PRELIMINARY PRODUCT SPECIFICATION
nRF24L01 Single Chip 2.4 GHz Radio Transceiver
1: PRX device:
The PRX device compares the received PID with the last PID. If the PID fields are
different, the packet is considered to be new. If the PID is equal to last received PID,
the received packet might be the same as last time. The receiver must check if the
CRC is equal to the previous CRC. If the CRC is equal to the previous one, the packet
is probably the same, and will be discarded.
2: PTX device:
The transmitter increments the PID field each time it sends a new packet.
TX side functionality
RX side functionality
Start
Start
New packet
from MCU?
PID equal
last PID?
CRC equal
last CRC?
Yes
Yes
Yes
increment PID
No
No
No
New packet is
valid for MCU
Discard packet
as a copy
End
End
Figure 6 PID generation/detection
The length of the CRC is configurable through the SPI interface. It is important to
notice that the CRC is calculated over the whole packet including address, PID and
payload. No packet is accepted as correct if the CRC fails. This is an extra
requirement for packet acceptance that is not illustrated in the figure above.
Stationary Disturbance Detection – CD
Carrier Detect (CD) is set high when an in-band RF signal is detected in RX mode,
otherwise CD is low. The internal CD signal is filtered before presented to CD
register. The internal CD signal must be high for at least 128µs.
In Enhanced ShockBurst™ it is recommended to use the Carrier Detect functionality
only when the PTX device does not succeed to get packets through, as indicated by
the MAX_RT interrupt for single packets and by the packet loss counter
(PLOS_CNT) if several packets are lost. If the PLOS_CNT in the PTX device
indicates too high rate of packet losses, the device can be configured to a PRX device
for a short time (Tstbt2a + CD-filter delay = 130µs+128µs = 258µs) to check CD. If CD
was high (jam situation), the frequency channel should be changed. If CD was low
Nordic Semiconductor ASA - Vestre Rosten 81, N-7075 Tiller, Norway
Revision: 1.1
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Phone +4772898900
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Fax +4772898989
November 2005
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