MRF24J40_08 Datasheet, PDF (114/152 Pages) Microchip Technology – IEEE 802.15.4™ 2.4 GHz RF Transceiver

MRF24J40
3.13 Acknowledgement
An Acknowledgment frame is used for confirming
successful frame reception. The successful reception of
a data or MAC command frame can be optionally
confirmed with an Acknowledgment frame. If the
originator does not receive an Acknowledgment after, at
most macAckWaitDuration (54) symbols, it assumes
that the transmission was unsuccessful and retries the
frame transmission. The turnaround time from the
reception of the packet to the transmission of the
Acknowledgment shall be less than aTurnaroundTime
(12) symbols. Acknowledgment frames are sent without
using a CSMA-CA mechanism. Refer to
IEEE 802.15.4-2003 Standard, Section 7.5.6.4 “Use of
Acknowledgments” for more information.
The MRF24J40 provides hardware support for:
• Acknowledgment Request – Originator
• Acknowledgment Request – Recipient
• Reception of Acknowledgment with Frame
Pending bit
• Transmission of Acknowledgment with Frame
Pending bit
These features are explained below.
3.13.1 ACKNOWLEDGMENT REQUEST –
ORIGINATOR
A data or MAC command frame, transmitted by an
originator with the Acknowledgment request subfield in
its frame control field set to ‘1’, shall be Acknowledged
by the recipient. The originator shall wait for at most
macAckWaitDuration (54) symbols for the
corresponding Acknowledgment frame to be received.
If an Acknowledgment is received, the transmission is
successful. If an Acknowledgment is not received, the
originator shall conclude that the transmission failed. If
the transmission was direct, the originator shall retrans-
mit the data or MAC command frame and wait. If
an Acknowledgment is not received after
aMaxFrameRetries (3) transmissions, the originator
shall assume the transmission has failed and notify the
upper layers of the failure.
The MRF24J40 features hardware retransmit. It will
automatically retransmit the packet if an Acknowledg-
ment has not been received. The Acknowledgment
request bit in the frame control field should be pro-
grammed into the transmit FIFO of interest and the
applicable xACKREQ bit should be set:
• TXNACKREQ (TXNCON 0x1B<2>) – When the
TX Normal FIFO transmits a frame, an
Acknowledgment frame is expected. If an
Acknowledgment is not received, retransmit.
• TXG1ACKREQ (TXG1CON 0x1C<2>) – When
the TX GTS1 FIFO transmits a frame, an
Acknowledgment frame is expected. If an
Acknowledgment is not received, retransmit.
• TXG2ACKREQ (TXG2CON 0x1D<2>) – When
the TX GTS2 FIFO transmits a frame, an
Acknowledgment frame is expected. If an
Acknowledgment is not received, retransmit.
When the frame is transmitted, the MRF24J40 will
expect an Acknowledgment frame within
macAckWaitDuration. If an Acknowledgment is not
received, it will retransmit aMaxFrameRetries.
The macAckWaitDuration value can be programmed
by the MAWD (ACKTMOUT 0x12<6:0>) bits.
The aMaxFrameRetries value is a constant and not
configurable. The number of retry times of the most
recent TXNFIFO transmission can be read in the
TXNRETRY (TXSTAT 0x24<7:6>) bits. The number of
retry times for the TX GTS1 FIFO and TX GTS2 FIFO
can be programmed or read in the TXG1RETRY
(TXG1CON 0x1C<7:6>) and TXG2RETRY (TXG2CON
0x1D<7:6>) bits.
DS39776B-page 112
Preliminary
© 2008 Microchip Technology Inc.