nRF24L01 Nordic VLSI, nRF24L01 Datasheet - Page 17

• Manufacturer Part Number: nRF24L01
• Manufacturer: Nordic VLSI

PRODUCT SPECIFICATION
nRF24L01 Single Chip 2.4 GHz Radio Transceiver
(i.e. the maximum number of sending is reached). The only way to reset this is to set
the PWR_UP bit low or let the auto retransmission finish. A packet loss counter will
be incremented each time a packet does not succeed to reach the destination before
time out. (Time out is indicated by the MAX_RT interrupt.) The packet loss counter is
reset when writing to the RF channel register.
TM
Packet Identity (PID) and CRC used by Enhanced ShockBurst
Each packet contains a two bit wide PID field to detect if the received packet is new
or resent. The PID will prevent that the PRX device presents the same payload more
than once to the micro controller. This PID field is incremented at the TX side for
each new packet received via the SPI interface. The PID and CRC field is used by the
PRX device to determine whether a packet is resent or new. When several data is lost
on the link, the PID fields may in some cases become equal to last received PID. If a
packet has the same PID as the previous packet, nRF24L01 will compare the CRC
sums from both packets. If they also are equal, the last received packet is considered
as a copy of the previous and is discarded.
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
PID equal
CRC equal
Yes
Yes
from MCU?
last PID?
last CRC?
Yes
increment PID
No
No
No
New packet is
Discard packet
valid for MCU
as a copy
End
End
Figure 6 PID generation/detection
Nordic Semiconductor ASA
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Page 17 of 43
Revision: 1.0
September 2006