XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
PRELIMINARY
REV. P1.0.1
236
4.3.1.2.1
AMI or Alternate Mark Inversion, means that consec-
utive one’s pulses (or marks) will be of opposite polar-
ity with respect to each other. This line code involves
the use of three different amplitude levels: +1, 0, and
-1. The +1 and -1 amplitude signals are used to rep-
resent one’s (or mark) pulses and the "0" amplitude
pulses (or the absence of a pulse) are used to repre-
sent zeros (or space) pulses. The general rule for the
AMI Decoding
AMI line code is: if a given mark pulse is of positive
polarity, then the very next mark pulse will be of nega-
tive polarity and vice versa. This alternating-polarity
relationship exists between two consecutive mark
pulses, independent of the number of zeros that exist
between these two pulses. Figure 83 presents an il-
lustration of the AMI Line Code as would appear at
the RxPOS and RxNEG input pins of the Framer, as
well as the corresponding output signal on the line.
N
OTE
:
One of the reasons that the AMI Line Code has
been chosen for driving copper medium, isolated via trans-
formers, is that this line code has no dc component, thereby
eliminating dc distortion in the line.
4.3.1.2.2
B3ZS Decoding
The Transmit DS3 LIU Interface block and the associ-
ated LIU embed and combine the data and clocking
information into the line signal that is transmitted to
the remote terminal equipment. The remote terminal
equipment has the task of recovering this data and
F
IGURE
82. I
LLUSTRATION
ON
HOW
THE
R
ECEIVE
DS3 F
RAMER
(
WITHIN
THE
XRT74L73 F
RAMER
IC)
BEING
INTER
-
FACED
TO
THE
XRT73L00 LIU,
WHILE
THE
F
RAMER
IS
OPERATING
IN
B
IPOLAR
M
ODE
(
ONE
CHANNEL
SHOWN
)
5V
U1
XRT72L5x
TxPOS
65
TxNEG
64
TxLineClk
63
DMO
79
ExtLOS
78
RLOL
77
LLOOP
69
RLOOP
70
TAOS
68
TxLEV
67
ENCODIS
66
REQB
71
RxPOS
76
RxNEG
75
RxLineClk
74
MOTO
27
RESETB
28
A0
A1
A2
A3
A4
A5
A6
A7
A8
15
16
17
18
19
20
21
22
23
D0
D1
D2
D3
D4
D5
D6
D7
32
33
34
35
36
37
38
39
Rdy_Dtck
6
WRB_RW
ALE_AS
7
10
9
CSB
8
INTB
13
TxSER
TxInClk
TxFrame
46
43
61
RxSer
RxFrame
86
88
90
RxLOS
RxOOF
RxRED
RxAIS
95
94
93
87
25
U2
XRT73L0x
TPDATA
37
TNDATA
38
TCLK
36
RCLK1
31
RNEG
32
RPOS
33
TTIP
41
TRING
40
MTIP
44
MRING
43
RRING
9
RTIP
8
DMO
4
RLOS
24
RLOL
23
LLB
14
RLB
15
TAOS
2
TxLEV
1
ENCODIS
21
REQDIS
12
T1
1:1
1
5
4
8
T2
1:1
1
5
4
8
R1
36
1
2
R2
36
1
2
R6
37.5
1
2
R3
270
1
2
R4
270
1
2
R5
37.5
1
2
C1
0.01uF
1
2
TxSER
TxInClk
TxFrame
NIBBLEINTF
RESETB
RTIP
RRING
CSB
RW
DS
AS
RxSer
RxFrame
RxLOS
RxRED
RxAIS
A[8:0]
TRING
TTIP
INTB
D[7:0]
F
IGURE
83. I
LLUSTRATION
OF
AMI L
INE
C
ODE
Data
1 0 1 1 0 0 0 1 0 1 1 1 1 0 1 1 0 1 1 0 0 1 1 0 0 0 0 1
RxPOS
RxNEG
Line Signal