XBee‐PRO®900HP/XBee‐PRO®XSCRFModules
©2014DigiInternationalInc. 33
3.XBee‐PRO900HPNetworkingMethods
This chapter will attempt to explain the basic layers and the three networking methods available on the XBee-PRO
®
900HP RF modules, building from the simplest to the most complex.
MAC/PHY Basics
PHY is short for Physical Layer. It is responsible for managing the hardware that modulates and demodulates the RF bits.
MAC stands for Media Access Layer. The MAC layer is responsible for sending and receiving RF frames. As part of each
packet, there is a MAC layer data header that has addressing information as well as packet options. This layer
implements packet acknowledgements (ACKs), packet tracking to eliminate duplicates, etc.
When a radio is transmitting, it cannot receive packets. When a radio is not sleeping, it is either receiving or
transmitting. There are no beacons or master/slave requirements in the design of the MAC/PHY.
This radio uses a patented method for scanning and finding a transmission. When a radio transmits, it sends out a
repeated preamble pattern, a MAC header, optionally a network header, followed then by packet data. A receiving radio
is able to scan all the channels to find a transmission during the preamble, then once it has locked into that it will
attempt to receive the whole packet.
Related parameters: CM, HP, ID, PL, RR, MT
The Preamble ID (HP) can be changed to make it so a group of radios will not interfere with another group of radios
in the same vicinity. The advantage of changing this parameter is that a receiving radio will not even lock into a
transmission of a transmitting radio that does not have the same ID.
The Network ID (ID) can be changed to further keep radios from interfering with each other. This ID is matched after
the preamble pattern has been matched, and the MAC header has been received. Networks are defined with a
unique network identifier. For modules to communicate they must be configured with the same network identifier.
The ID parameter allows multiple networks to co-exist on the same physical channel.
The Channel Mask (CM) parameter determines the channels that the radio will choose to communicate on. See CM in
the command reference.
Power Level (PL) sets the TX power level. The power level can be reduced from the maximum to reduce current con-
sumption or for testing. This comes at the expense of reduced radio range.
The RR parameter specifies the number of time a sending radio will attempt to get an ACK from a destination radio
when sending a packet.
The MT parameter specifies the number of times that a broadcast packet is repeatedly transmitted. This adds redun-
dancy that improves reliability.
XBee-PRO 900HP Addressing Basics
Related parameters: SH, SL, DH, DL, TO
64-bit Addresses
Each radio is given a unique IEEE 64-bit address at the factory. This can be read with the SH and SL com-
mands. This is the source address that is returned in API mode of the radio that sent a packet. At this time
addresses are of the form: 0x0013A2XXXXXXXXXX. The first 6 digits are the Digi (MaxStream) OUI. The
broadcast address is 0x000000000000FFFF.
Unicast
To transmit to a specific radio:
• When using transparent mode set DH:DL to the SH:SL of the destination radio.
• For API mode, set the SH:SL address in the 64-bit destination address.
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