A24-HASM-525 Digi International/Maxstream, A24-HASM-525 Datasheet - Page 22

• Manufacturer Part Number: A24-HASM-525
• Description: ANT 2.4GHZ 6" DIPOLE OMNI DIRECT
• Manufacturer: Digi International/Maxstream
• Series: XPressr

Specifications of A24-HASM-525

• Antenna Type: Whip: Swivel, Tilt (Right Angle)
• Number Of Bands: 1
• Frequency: 2.4GHz
• Gain: 2.1dBi
• Termination: RP-SMA
• Mounting Type: Connector
• Height (max): 5.98" (152mm)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Vswr: -
• Other names: A09-HASM-525; A09-HASM-525

XBee®/XBee‐PRO® RF Modules ‐ 802.15.4 ‐ v1.xEx [2009.09.23]
CCA (Clear Channel Assessment)
Acknowledgement
Direct Transmission
A Coordinator can be configured to use only Direct Transmission by setting the SP (Cyclic Sleep
Period) parameter to "0". Also, a Coordinator using indirect transmissions will revert to direct
transmission if it knows the destination module is awake.
To enable this behavior, the ST (Time before Sleep) value of the Coordinator must be set to match
the ST value of the End Device. Once the End Device either transmits data to the Coordinator or
polls the Coordinator for data, the Coordinator will use direct transmission for all subsequent data
transmissions to that module address until ST time occurs with no activity (at which point it will
revert to using indirect transmissions for that module address). "No activity" means no transmis-
sion or reception of messages with a specific address. Global messages will not reset the ST timer.
Indirect Transmission
To configure Indirect Transmissions in a PAN (Personal Area Network), the SP (Cyclic Sleep Period)
parameter value on the Coordinator must be set to match the longest sleep value of any End
Device. The sleep period value on the Coordinator determines how long (time or number of bea-
cons) the Coordinator will retain an indirect message before discarding it.
An End Device must poll the Coordinator once it wakes from Sleep to determine if the Coordinator
has an indirect message for it. For Cyclic Sleep Modes, this is done automatically every time the
module wakes (after SP time). For Pin Sleep Modes, the A1 (End Device Association) parameter
value must be set to enable Coordinator polling on pin wake-up. Alternatively, an End Device can
use the FP (Force Poll) command to poll the Coordinator as needed.
Prior to transmitting a packet, a CCA (Clear Channel Assessment) is performed on the channel to
determine if the channel is available for transmission. The detected energy on the channel is com-
pared with the CA (Clear Channel Assessment) parameter value. If the detected energy exceeds
the CA parameter value, the packet is not transmitted.
Also, a delay is inserted before a transmission takes place. This delay is settable using the RN
(Backoff Exponent) parameter. If RN is set to “0”, then there is no delay before the first CCA is per-
formed. The RN parameter value is the equivalent of the “minBE” parameter in the 802.15.4 spec-
ification. The transmit sequence follows the 802.15.4 specification.
By default, the MM (MAC Mode) parameter = 0. On a CCA failure, the module will attempt to re-
send the packet up to two additional times.
When in Unicast packets with RR (Retries) = 0, the module will execute two CCA retries. Broadcast
packets always get two CCA retries.
If the transmission is not a broadcast message, the module will expect to receive an acknowledge-
ment from the destination node. If an acknowledgement is not received, the packet will be resent
up to 3 more times. If the acknowledgement is not received after all transmissions, an ACK failure
is recorded.
© 2009 Digi Internatonal, Inc.
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