XBee‐PRO®900HP/XBee‐PRO®XSCRFModules
©2014DigiInternationalInc. 136
After receiving and acknowledging a packet, the receiving module will move to the next frequency
and listen for either a retransmission or new data for a specific period of time. Even if the
transmitting module has indicated that it has no more pending transmit data, it may have not
received the previous ACK, and so it may retransmit the packet (potentially with no delay after the
ACK slot). In this case, the receiving module will always detect the immediate retransmission,
which will hold off the communications channel and thereby reduce collisions. Receiving modules
acknowledge each retransmission they receive, but they only pass the first copy of a packet they
receive out the UART. RB and RO parameters are not applied to subsequent packets. This means
that once transmission has begun, it will continue uninterrupted until the DI buffer is empty or the
streaming limit (TT) has been reached. As with the first packet, the payload of each subsequent
packet includes up to the maximum packet size (PK parameter). The transmitting module checks
for more pending data near the end of each packet. The streaming limit (TT parameter) specifies
Idle
Mode
Inhibit
Transmission
for RN Delay
DI Buer?
DI Buer?
Discard Packet
Reset Retry
Count (RR)
Increment TX
Failure Count
(TR)
RB Chars?
RD Char
times of
Silence?
Initialize
Channel (sync)
Assemble
Packet
Transmit Packet
ACK
Received?
RR
Expired?
Initialize
Inhibit
Transmission
for RN Delay
Slots
Decrement
Retry Count
(RR)
Reset IT Counter
Yes
No
Yes
Yes
No
No Yes
Yes
Yes
No
Yes
No
No
No
Detected
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