XRT74L74 Datasheet, PDF(347/498 Page) Exar Corporation – 4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

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XRT74L74 Datasheet, PDF (347/498 Pages) Exar Corporation – 4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

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PRELIMINARY

XRT74L74

4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

REV. P1.1.1

FIGURE 137. ILLUSTRATION ON HOW A CHANNEL OF THE RECEIVE E3 FRAMER (WITHIN THE XRT74L74 FRAMER

IC) BEING INTERFACE TO THEXRT73L00 LINE INTERFACE UNIT, WHILE OPERATING IN BIPOLAR MODE

TxSER

TxInClk

TxFrame

NIBBLEINTF

RESETB

INTB

CSB

RW

DS

AS

INTB

A[8:0]

D[7:0]

5V

RxSer

RxClk

RxFrame

RxLOS

RxOOF

RxRED

RxAIS

U1

46

43

TxSER

61 TxInClk

TxFrame

25

NIBBLEINTF

28

RESETB

13

8 INTB

7

10

CSB

WRB_RW

9 RDB_DS

6

ALE_AS

Rdy_Dtck

15

16

17

A0

A1

18 A2

19 A3

20 A4

21 A5

22

23

A6

A7

A8

32

33 D0

34

35

D1

D2

36 D3

37

38

D4

D5

39 D6

D7

27

MOTO

86

88

RxSer

90 RxClk

RxFrame

95

94 RxLOS

93 RxOOF

87 RxRED

RxAIS

XRT74L74

TxPOS 65

64

TxNEG

63

TxLineClk

79

DMO

78

ExtLOS

RLOL 77

LLOOP 69

70

RLOOP

68

TAOS

TxLEV 67

66

ENCODIS

REQB 71

76

RxPOS

75

RxNEG

RxLineClk 74

U2

37 TPDATA

38

TNDATA

36

TCLK

4

DMO

24

RLOS

23 RLOL

14 LLB

15

RLB

2

TAOS

1 TxLEV

21

ENCODIS

12 REQDIS

33

RPOS

32

RNEG

31 RCLK1

XRT73L00

TTIP 41

40

TRING

44

MTIP

MRING 43

1 R3 2

270

1 R4 2

270

R1

1

2

36

1 T1 5

R2

1

2

36

4

8

1:1

TTIP

TRING

8

RTIP

RRING 9

C1

12

0.01uF

R5

37.5

R6

37.5

1 T2 5

4

8

1:1

RTIP

RRING

6.3.1.2.1 AMI Decoding

AMI or Alternate Mark Inversion, means that consec-

utive "oneâs" 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 oneâs (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 138 presents an il-

lustration 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.

345

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