XRT72L50 Datasheet, PDF (435/471 Pages) Exar Corporation – SINGLE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
FIGURE 189. FLOW CHART DEPICTING THE FUNCTIONALITY OF THE LAPD RECEIVER
START
Enable the LAPD R eceiver
This is done by writing the value 0xFC into
the R xLAPD Control R egister (Adress =
0x18)
LAPD R eceiver begins reading in theN R or
G C byte field from each inbound E3 fram e.
Does
LAPD R eceiver
detect
6 C onsecutive
"O ne s"?
Destuff "Zeros"
NO
after any 5
C onsecutive
"O ne s"
YES
R eceive LAPD
Message
1
1
W rite
0x7E
to
0xDE
First Flag
Sequence is
R eceived
NO
H as first
Flag Sequence
been received?
NO
YES
YES
ABORT
Does
LAPD R eceiver
detect
7 C onsecutive
"O ne s"?
Does
LAPD R eceiver
detect
6 C onsecutive
"O ne s"?
Resart
search for
First Flag
Sequence
YES
1
Does
LAPD R eceiver
detect
7 C onsecutive
"O ne s"?
YES
1
Execute LAPD
R eceived
In te rru p t
S e rv ic e
R outine
FCS error
bit "H igh"
NO
Is FCS
verifiy
OK?
YES
G e n e rate
LAPD
R eceiver
in te rru p t
1
NO
End of Message
W rite Received
LAPD Message
to M essage Buffer
(0xDF thru 0x135)
Com pute &
Verify FCS
based on
m essage length
by m essage type
6.3.4 The Receive Overhead Data Output Interface
Figure 190 presents a simple illustration of the Receive Overhead Data Output Interface block within the
XRT72L50.
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