XStream-PKG-R™ RS-232/485 RF Modem – Product Manual v5.x00
Figure 3.4.
Data Transmission Sequence
RF D a t a Pa ck e t
The RF pack et is t he sequence of dat a used for com m unicat ing infor m at ion bet ween Digi
Modem s. An RF Pack et consists of an RF I nit ializer and RF Dat a.
Figure 3.5.
RF Data Packet Components
* When st ream ing m ult iple RF pack et s, t he RF I nit ializer is only sent in front of t he fir st pack et .
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 r eceiv ing m odem s of inform at ion such as t he hopping pat t er n
used by t he tr ansm it t ing m odem . The fir st t r ansm ission alway s sends an RF init ializer .
An RF init ializer can be of v ar ious lengt hs depending on t he am ount of t im e det er m ined t o be
r equired t o prepar e a r eceiv ing m odem . For ex am ple, a w ak e- up init ializer is a t ype of RF
init ializer used t o w ak e r em ote m odem s from Sleep Mode ( Refer t o t he FH, LH, HT and SM
Com m ands for m or e infor m at ion) . The lengt h of t he w ake- up init ializer should be longer t han t he
lengt h of t im e r em ot e m odem s are in cy clic sleep.
H e a de r
The header cont ains net work addressing infor m at ion t hat filt er s incom ing RF dat a. The r eceiv ing
m odem checks for a m at ching Hopping Channel ( HP par am et er ) , Vendor I dent ificat ion Num ber
( I D par am et er ) and Dest inat ion Address ( DT par am et er ) . Dat a t hat does not pass t hrough all
t hr ee net wor k filt er lay er s is discar ded.
CRC ( Cy clic Re du n da n cy Ch e ck )
To v er ify dat a int egr it y and prov ide built - in er r or check ing, a 16- bit CRC ( Cy clic Redundancy
Check ) is com put ed for t he t ransm it t ed dat a and at t ached to t he end of each RF packet . On t he
r eceiv ing end, t he r eceiv ing m odem com put es t he CRC on all incom ing RF dat a. Received dat a
t hat has an inv alid CRC is discar ded ( Refer t o t he Receiv e Mode sect ion, nex t page) .
© 2014 Digi International Inc.
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