MRF24XA_15 Datasheet, PDF (189/258 Pages) Microchip Technology – Low-Power, 2.4 GHz ISM-Band IEEE 802.15.4™ RF

MRF24XA
7.0 ADVANCED LINK BEHAVIOR
IN PROPRIETARY PACKET
MODE
7.1 Channel Agility
In some communication environments, where several
nodes use the same medium, it is necessary to choose
different channels for the communicating nodes. It
introduces difficulties in ACK receiving. Figure 7-1 illus-
trates the example of channel agility. To prevent higher
MCU load on channel changing, MRF24XA handles
the channel change for the automatic sending of ACK.
This feature is enabled by ADPTCHEN bit that must be
enabled for all the nodes within the same network.
Figure 4-13 describes the ACK sending mechanism.
FIGURE 7-1:
CHANNEL AGILITY EXAMPLE
Interfering
Node
Channel: 10
Note that in case of Inferred DA, the ACKINFO field is
mandatory when AckReq=1. Otherwise the ACKINFO
field is mandatory if ADPTDREN = 1 or ADPTCHEN =
1.
Interfering
Node
Channel: 7
Node A
Node B
RX Channel: 7
RX Channel: 10
EXAMPLE 7-1: AUTO ACK EXAMPLE WITH CHANNEL AGILITY
A
B:
A: CHANNEL = 10⁽¹⁾
B: CHANNEL = 10⁽²⁾
RXIF
TXST
CHANNEL = 7
CHANNEL = 7
Sending ACK back to A
CHANNEL = 10
Note 1: Node A knows the frequency channel that Node B uses for receiving.
2: However, Node B knows the RX channel of Node A, as AUTOACK = 1 the ACK must immediately sent
back, and there is no time for MCU interactions.
Channel Agility is based on AckInfo field of the Propri-
etary MAC header. Proprietary MAC header is
described in Figure 6-1.
FIGURE 7-2:
PROPRIETARY MAC ACKINFO<7:0> OCTET (ONLY PRESENT WHEN ACKREQ = 1)
3:0
7:4
ACKDataRate
(4 bits)
ACKChannel
(4 bits)
1 Octet
AckDataRate: When ADPTDREN = 1 and AckReq = 1, this field determines the TX Data Rate for the ACK packet,
regardless of the setting of the DR<3:0> Register field.
AckChannel: When ADPTCHEN = 1 and AckReq = 1, this field determines the TX Channel for the ACK packet,
regardless of the setting of the CH<3:0> register field.
 2015 Microchip Technology Inc.
Preliminary
DS70005023C-page 189