MRF24XA_15 Datasheet, PDF (97/258 Pages) Microchip Technology – Low-Power, 2.4 GHz ISM-Band IEEE 802.15.4™ RF

4.3 Global vs. Per Node vs. Per Packet
Configurations
For certain configurable parameters, the selected
options apply to all nodes in a network. The following
are the global attributes:
• The MAC frame format used in the network
(FRMFMT register bit configuration)
• The FCS appending and checking method (refer
to CRCSZ register bit)
• The medium access (CSMAEN register bit config-
uration
4.3.1 GLOBAL CONFIGURATIONS
Global attributes are negotiated through management
information travelling in the MAC payload (of the
current frame or a previous frame). For example,
• Address size in Proprietary MAC framing mode
• Network Layer security enabling and security
material in IEEE 802.15.4-compliant MAC framing
mode
These global attributes are shared between all nodes
of the network as all the nodes can access the same
medium, and the sending and recipient sides must
process the frame consistently.
4.3.2 PER PACKET CONFIGURATIONS
As opposed to global configurations, per packet
attributes vary from packet to packet. For example,
• Acknowledge Requested for the current frame
(AckReq)
• Security Processing enabled for the current frame
(SecEn)
These attributes must be shared between the originator
and the recipient of the frame and must travel with the
packet. Prior sending a frame, the originator MCU
applies the desired attributes when the respective
frame control bits (for example, AckReq, SecEn) in the
MAC header of the frame are configured. When the
send operation is triggered, the sending device checks
these attributes and adapts its (frame processing and
sending) behavior accordingly. The receiver device
does the same on reception.
4.3.3 PER NODE CONFIGURATION
It applies to specific nodes in the network, having a
specific role. The auto-repeater functionality (in
proprietary MAC mode) is a typical example. Another
case is how a node filters frames. A sniffer node must
have different Configuration than an ordinary node.
This Configuration may also be different since the
sniffer must not send acknowledge.
MRF24XA
4.4 Features Overview
The device supports two Framing modes:
• IEEE 802-15.4 standard compliant, see
Section 5.0 “IEEE 802.15.4™ Compliant Frame
Format and Frame Processing” format
• Proprietary format, see Section 6.0 “Proprietary
Frame Format and Frame Processing”
Hardware support is provided for both the features, but
a network must only use one of these in all the nodes.
A compromise is offered through Bridging, see
Section 8.0 “Bridging”.
For the discussion it is helpful to distinguish between
Protocol Agnostic and Protocol Dependent.
Configuration Options:
• The availability and Configuration format of Proto-
col Dependent options are conditioned on the
selected framing protocol whether IEEE 802.15.4-
compliant or proprietary network operation is
required.
• In contrast, the availability, behavior and Configu-
ration format of other options are Protocol
Agnostic from a device point of view, which
means that the Configuration occurs similarly for
framing protocol.
All Protocol Agnostic options can freely combined with
any of the “protocol-dependent” configurations as far
as the device constrains it. To comply with the IEEE
802.15.4 protocol, the constraints specified in the stan-
dards must be followed, see Table 4-3.
Figure 4-6 lists the higher level (MAC layer) Configura-
tion features.
• FCS method: Hardware supports the 2-byte long
CRC sequence adopted by IEEE 802-15.4. This
must be adequate for most applications. In the
contrary case, the CRC appending and checking
are disabled if CRCSZ = 0. If CRCSZ = 0 then
AUTOACKEN = 0 and RXFILTER = 0x00 is
required. CRCSZ = 1 is assumed in the discus-
sion.
• CSMA is described in Section 4.11 “Carrier
Sense Multiple Access-Collision Avoidance
(CSMA-CA)” and only requires Packet mode.
• Automatic Acknowledgement Reception and
Sending is configured as specified in
Section 4.12 “Clear Channel Assessment
(CCA)”, Section 4.14 “Acknowledge Sending
by Recipient” and Section 4.15 “Acknowledge
Reception by Originator”.
 2015 Microchip Technology Inc.
Preliminary
DS70005023C-page 97