MaxStream 9 XTend- PKG- E, Manual

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9XTend
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PKG
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E™ Ethernet RF Modem – Product Manual v2.x4x [2007.01.04]
© 2007 MaxStream, Inc., Confidential & Proprietary
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All Rights Reserved 15
Channel init ializat ion is t he process of sending an RF init ializer t hat synchr onizes r eceiving
m odem s w it h t he t ransm it t ing m odem . During channel init ializat ion, incom ing serial dat a accum u-
lat es in t he DI buffer.
RF dat a, w hich includes t he payload dat a, follow s t he RF init ializer. The payload includes up t o t he
m axim um packet size ( PK Com m and) byt es. As t he TX m odem nears t he end of t he t ransm ission,
it inspect s t he DI buffer t o see if m ore dat a exist s t o be t ransm it t ed. This could be t he case if m ore
t han PK byt es were originally pending in t he DI buffer or if m ore byt es arrived from t he UART aft er
t he t ransm ission began. I f m ore dat a is pending, t he t ransm it t ing m odem assem bles a subsequent
packet for t ransm ission.
Refer t o t he ‘RF Com m unicat ion Modes’ sect ion t o view st at e diagram s t hat illust rat e channel ini-
t ializat ion and t he sequence of event s t hat follow.
RF Pa ck e t
Figure 3
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03. RF Packet Components
* When streaming multiple RF packets, the RF Initializer is only sent in front of the first packet.
RF I n it ia liz e r
An RF init ializer is sent each t im e a new connect ion sequence begins. The RF init ializer cont ains
channel inform at ion t hat not ifies receiving m odem s of inform at ion such as t he hopping pat t ern
used by t he t ransm it t ing m odem . The first t ransm ission always sends an RF init ializer.
An RF init ializer can be of various lengt hs depending on t he am ount of t im e det erm ined t o be
required t o prepare a receiving m odem . For exam ple, a wake- up init ializer is a t ype of RF init ializer
used t o wake rem ot e m odem s from Sleep Mode ( Refer t o t he FH, LH, HT and SM Com m ands for
m ore inform at ion) . The lengt h of t he wake- up init ializer should be longer t han t he lengt h of t im e
rem ot e m odem s are in cyclic sleep.
H e a de r
The header cont ains net w ork addressing inform at ion t hat filt ers incom ing RF dat a. The receiving
m odem checks for m at ching a Hopping Channel, VI D and Dest inat ion Address. Dat a t hat does not
pass t hrough all t hree net w ork filt er layers is discarded.
Refer t o t he ‘Addressing’ sect ion of t he “ RF Com m unicat ion Modes” chapt er for m ore inform at ion.
CRC ( Cy clic Re dun da n cy Che ck )
To verify dat a int egrit y and provide built - in error checking, a 16- bit CRC ( Cyclic Redundancy
Check) is com put ed for t he t ransm it t ed dat a and at t ached t o t he end of each RF packet . On t he
r eceiving end, t he r eceiving m odem com put es t he CRC on all incom ing RF dat a. Received dat a t hat
has an invalid CRC is discarded [ refer t o t he ‘Receive Mode’ sect ion] .