Datasheet

PRELIMINARY PRODUCT SPECIFICATION
nRF24L01 Single Chip 2.4 GHz Radio Transceiver
Nordic Semiconductor ASA - Vestre Rosten 81, N-7075 Tiller, Norway - Phone [phone] - Fax [phone]
Revision: 1.2 Page 16 of 39 March 2006
(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.
Packet Identity (PID) and CRC used by Enhanced ShockBurst
TM
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 microcontroller. 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.
Start
New packet
from MCU?
Yes
increment PID
End
Start
PID equal
last PID?
Yes
CRC equal
last CRC?
New packet is
valid for MCU
End
No
Discard packet
as a copy
No
Yes
TX side functionality RX side functionality
No
Figure 6 PID generation/detection