
XRT7250
á
DS3/E3 FRAMER IC
REV. 1.1.1
286
5.3.1.2.1
AMI Decoding
AMI or Alternate Mark Inversion, means that consec-
utive "one's" pulses (or marks) will be of opposite po-
larity with respect to each other. This line code in-
volves the use of three different amplitude levels: +1,
0, and -1. The +1 and -1 amplitude signals are used
to represent one's (or mark) pulses and the "0" ampli-
tude pulses (or the absence of a pulse) are used to
represent zeros (or space) pulses. The general rule
for AMI is: if a given mark pulse is of positive polarity,
then the very next mark pulse will be of negative po-
larity and vice versa. This alternating-polarity rela-
tionship exists between two consecutive mark pulses,
independent of the number of zeros that exist be-
tween these two pulses.
Figure 131 presents an illus-
tration of the AMI Line Code as would appear at the
RxPOS and RxNEG pins of the Framer, as well as the
output signal on the line.
NOTE: 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.
FIGURE 130. ILLUSTRATION ON HOW THE RECEIVE E3 FRAMER (WITHIN THE XRT7250 FRAMER IC) BEING INTER-
FACE TO THE
XRT7300 LINE INTERFACE UNIT, WHILE THE FRAMER IS OPERATING IN BIPOLAR MODE
5V
U1
XRT7250
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
15
A1
16
A2
17
A3
18
A4
19
A5
20
A6
21
A7
22
A8
23
D0
32
D1
33
D2
34
D3
35
D4
36
D5
37
D6
38
D7
39
Rdy_Dtck
6
WRB_RW
7
RDB_DS
10
CSB
8
ALE_AS
9
INTB
13
TxSER
46
TxInClk
43
TxFrame
61
RxSer
86
RxClk
88
RxFrame
90
RxLOS
95
RxOOF
94
RxRED
93
RxAIS
87
NIBBLEINTF
25
U2
XRT7300
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
NIBBLEINTF
RESETB
RTIP
RRING
CSB
RW
DS
AS
TxFrame
RxSer
RxClk
RxFrame
RxLOS
RxOOF
RxRED
RxAIS
A[8:0]
TRING
TTIP
INTB
D[7:0]
INTB
FIGURE 131. ILLUSTRATION OF AMI LINE CODE
Data
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
RxPOS
RxNEG
Line Signal