XStream‐PKG‐E™ Ethernet RF Modem – Product Manual v4.2B5
3 .2 . Tr a n sm it M ode
When t he fir st by t e of ser ial dat a is r eceiv ed from t he UART in t he DI buffer , t he m odem
at t em pt s to shift t o Tr ansm it Mode and init iat e an RF connect ion w it h ot her m odem s.
Figure 3‐02. Transmission of Data
Once in Tr ansm it Mode, t he
m odem init ializes a
com m unicat ions channel.
Channel init ializat ion is t he
process of sending an RF
init ializer t hat sy nchronizes
r eceiv ing m odem s w it h t he
t r ansm it t ing m odem . When
st ream ing m ult iple RF packet s,
t he RF I nit ializer is only sent in
front of t he first pack et . Dur ing
channel init ializat ion, incom ing
ser ial dat a accum ulat es in t he
DI buffer .
Aft er t he channel is init ialized,
dat a in t he DI buffer is
grouped int o pack et s ( up t o 64
by tes in each packet ) and is t ransm it ted. The m odem cont inues t o tr ansm it dat a packet s unt il t he
DI buffer is em pt y . Once t r ansm ission is finished, t he m odem r et ur ns t o I dle Mode. This
progr ession is show n abov e.
As t he t r ansm it t ing m odem nears t he end of t he tr ansm ission, it inspect s t he DI buffer to see if
m ore dat a ex ist s t o be t r ansm itt ed. This could be t he case if m ore by t es ar riv ed from t he host
aft er t he t r ansm ission began. I f m ore dat a is pending, t he transm it t ing m odem assem bles a
subsequent pack et for t r ansm ission.
3 .2 .1 . RF 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 Packet consist s of an RF I nit ializer and RF Dat a.
Figure 3‐03. 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 infor m at ion t hat not ifies r eceiving m odem s of inform at ion such as t he hopping pat t er n
used by the t ransm it t ing m odem . The fir st tr ansm ission alw ay 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 equir ed to pr epar e a receiv ing m odem . For ex am ple, a w ake- up init ializer is a ty pe of RF
init ializer used to w ak e r em ote m odem s fr om 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 w ake- up init ializer should be longer than t he
lengt h of t im e rem ot e m odem s are in cy clic sleep.
© 2014 Digi International Inc.
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