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XBee Series 2 OEM RF Modules ‐ ZigBee ‐ v1.x2x [2007.07.019]
2.2. Modes of Operation
2.2.1. Idle Mode
2.2.2. Transmit Mode
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When not receiving or transmitting data, the RF module is in Idle Mode. During Idle Mode, the RF
module is also checking for valid RF data. The module shifts into the other modes of operation
under the following conditions:
• Transmit Mode (Serial data in the serial receive buffer is ready to be packetized)
• Receive Mode (Valid RF data is received through the antenna)
• Sleep Mode (End Devices only)
• Command Mode (Command Mode Sequence is issued)
When serial data is received and is ready for packetization, the RF module will exit Idle Mode and
attempt to transmit the data. The destination address determines which node(s) will receive the
data.
Prior to transmitting the data, the module ensures that a 16-bit network address and route to the
destination node have been established.
If the 16-bit network address is not known, network address discovery will take place. If a route is
not known, route discovery will take place for the purpose of establishing a route to the
destination node. If a module with a matching network address is not discovered, the packet is
discarded. The data will be transmitted once a route is established. If route discovery fails to
establish a route, the packet will be discarded.
Figure 2‐04. Transmit Mode Sequence
16-bit Network
Idle Mode
Address Known?
New
Transmission
No
16-bit Network
Address Discovery
16-bit Network
Address Discovered?
No
Data Discarded
When data is transmitted from one node to another, a network-level acknowledgement is
transmitted back across the established route to the source node. This acknowledgement packet
indicates to the source node that the data packet was received by the destination node. If a
network acknowledgement is not received, the source node will re-transmit the data. See Data
Transmission and Routing in chapter 3 for more information.
© 2007 Digi International, Inc.
Successful
Transmission
Yes
Yes
Route Known?
No
Route Discovery
Yes
Yes
Route Discovered?
No
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Chapter 2 ‐ RF Module Operation
Transmit Data
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13
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