Data Sheet

Revision 2.0 Page 41 of 74
nRF24L01 Product Specification
7.9.2 Single transaction with a lost packet
Figure 16. is a scenario where a retransmission is needed due to loss of the first packet transmit. After the
packet is transmitted, the PTX enters RX mode to receive the ACK packet. After the first transmission, the
PTX waits a specified time for the ACK packet, if it is not in the specific time slot the PTX retransmits the
packet as shown in Figure 16.
Figure 16. TX/RX cycles with ACK and the according interrupts when the first packet transmit fails
When an address is detected the PTX stays in RX mode until the packet is received. When the retransmit-
ted packet is received by the PRX (see Figure 16.
), the RX_DR IRQ is asserted and an ACK is transmitted
back to the PTX. When the ACK is received by the PTX, the TX_DS IRQ is asserted.
7.9.3 Single transaction with a lost ACK packet
Figure 17. is a scenario where a retransmission is needed after a loss of the ACK packet. The correspond-
ing interrupts are also indicated.
Figure 17. TX/RX cycles with ACK and the according interrupts when the ACK packet fails
TX:PID=1 RX
PTX
PRX
RX ACK:PID=1
DL
MCU PRX
UL
MCU PTX
130us
1
TX:PID=1
RX
IRQ
ARD
Auto retransmit delay
elapsed
No address detected.
RX off to save current
Retransmit of packet
PID=1
Packet PID=1 lost
during transmission
Packet received.
IRQ: RX DR (PID=1)
ACK received
IRQ: TX DS (PID=1)
130us
1
130us
1
1 Radio Turn Around Delay
TX:PID=1 RX
PTX
PRX
RX ACK:PID=1
DL
MCU PRX
UL
MCU PTX
130us
1
TX:PID=1 RX
IRQ
ARD
Auto retransmit delay
elapsed
No address detected.
RX off to save current
Retransmit of packet
PID=1
ACK PID=1 lost
during transmission
Packet received.
IRQ: RX DR (PID=1)
ACK received
IRQ: TX DS (PID=1)
ACK:PID=1 RX
Packet detected as
copy of previous,
discarded
130us
1
130us
1
1 Radio Turn Around Delay