SETUP_RETR Register

Address

0x04

Description

The SETUP_RETR register is used to configure the delay between auto-retransmits and the number of times that a packet is retransmitted if the ack isn’t received.

Contents

This table is copied from the nRF24L01 product specification (page 54).

Name
Bit
Reset Value
Type Description
ARD 7:4 0000 R/W Auto Retransmit Delay
‘0000’ – Wait 250µS
‘0001’ – Wait 500µS
‘0010’ – Wait 750µS
……..
‘1111’ – Wait 4000µS
(Delay defined from end of transmission to start
of next transmission)
ARC 3:0 0011 R/W Auto Retransmit Count
‘0000’ –Re-Transmit disabled
‘0001’ – Up to 1 Re-Transmit on fail of AA
……
‘1111’ – Up to 15 Re-Transmit  on fail of AA

Comments

By default, the software driver uses a delay of 500µS and retransmits up to 5 times.  The 250µS delay is too short for acks with payloads of more than 15 bytes, which take more than 250µS to transmit at 1 Mbps.  Packets of any size are transmissible at any on-air data rate in 500µS.

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