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XRT72L50
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SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
211
NOTES:
1.
The white (e.g., unshaded) boxes reflect tasks that the user’s system must perform in order to configure the LAPD
Receiver to receive LAPD Messages.
2.
A brief description of the steps that must exist within the Receive LAPD Interrupt Service routine exists in
4.3.4
The Receive Overhead Data Output Interface
FIGURE 74. FLOW CHART DEPICTING THE FUNCTIONALITY OF THE LAPD RECEIVER
E n a b le th e L AP D R e ce iver
T his is do ne b y w riting the value 0 xF C in to
the R xLA P D C ontrol R eg ister (A dres s =
0x 18)
LA P D R ec eiver be gins rea ding in the D L
bits fro m ea ch inbo und D S3 fram e.
Has first
F la g S eq uenc e
be en re ceived ?
D oes
LAPD R ec eiver
de tect
6 C on sec utive
"O n es"?
D oes
LAPD R ec eiver
de tect
7 C on sec utive
"O n es"?
D oes
LAPD R ec eiver
de tect
6 C on sec utive
"O n es"?
D oes
LAPD R ec eiver
de tect
7 C on sec utive
"O n es"?
Is F C S
ve rifiy
OK ?
Write
0x 7E
to
0x D E
F C S error
bit "H igh"
C o m pute &
Ve rify FCS
ba sed on
m e ssa ge leng th
by m e ssa ge type
W rite R e ce ived
L A P D M e s sag e
to M es sag e B uffer
(0x D F thru 0 x13 5)
End of M e s s a g e
R ece ive LA P D
M e ss age
D estuff "Z e ros"
after any 5
C ons ecu tive
"O n es"
Firs t Flag
S eq uenc e is
Rece ived
Ex ec ute LA PD
R ece iv ed
In te rrupt
Se rv ic e
R outin e
Ge n e ra te
LA PD
R ece iv er
in te rrupt
ST A R T
AB O R T
Resa rt
se arch for
Firs t Flag
S eq uenc e
1
YES
NO