XRT74L73 Datasheet, PDF (224/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
PRELIMINARY
TX DS3 F-BIT MASK4 REGISTER, ADDRESS = 0X39
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT2
BIT 1
BIT 0
FBit Mask(7) FBit Mask(6) FBit Mask(5) FBit Mask(4) FBit Mask(3) FBit Mask(2) FBit Mask(1) FBit Mask(0)
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
0
0
0
0
0
0
0
0
4.2.5 The Transmit DS3 Line Interface Block
The XRT74L73 Framer IC is a digital device that
takes DS3 payload and overhead bit information from
some terminal equipment, processes this data and ul-
timately, multiplexes this information into a series of
outbound DS3 frames. However, for DS3 coaxial ca-
ble applications, the XRT74L73 Framer IC lacks the
current drive capability to be able to directly transmit
this DS3 data stream through some transformer-cou-
pled coax cable with enough signal strength for it to
comply with the Isolated Pulse Template require-
ments and be received by the remote receiver.
Therefore, in order to get around this problem, the
Framer IC requires the use of an LIU (Line Interface
Unit) IC. An LIU is a device that has sufficient drive
capability, along with the necessary pulse-shaping
circuitry to be able to transmit a signal through the
transmission medium in a manner that it can (1) com-
ply with the DSX-3 Isolated Pulse Template require-
ments and (2) be reliably received by the Remote Ter-
minal Equipment. Figure 72 presents a circuit draw-
ing depicting the Framer IC interfacing to an LIU
(XRT7300 DS3/E3/STS-1 Transmit LIU).
FIGURE 72. APPROACH TO INTERFACING THE XRT74L73 FRAMER IC TO THE XRT73L0X DS3/E3/STS-1 TRANS-
MITTER LIU (ONE CHANNEL SHOWN)
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 ^CSB
10 ^WRB_RW
9 ^RDB_DS
6 ^ALE_AS
Rdy_Dtck
15
16 ^A0
17 ^A1
18 ^A2
19 ^A3
20 ^A4
21 ^A5
22 ^A6
23 ^A7
A8
32
33 ^D0
34 ^D1
35 ^D2
36 ^D3
37 ^D4
38 ^D5
39 ^D6
D7
27
MOTO
86
88 ^RxSer
90 ^RxClk
RxFrame
95
94 ^RxLOS
93 ^RxOOF
87 ^RxRED
RxAIS
XRT72L5x
65
TxPOS
64
TxNEG
63
TxLineClk
79
DMO
78
ExtLOS
77
RLOL
69
LLOOP
70
RLOOP
68
TAOS
67
TxLEV
66
ENCODIS
71
REQB
76
RxPOS
75
RxNEG
74
RxLineClk
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
XRT73L0x
41
TTIP
40
TRING
44
MTIP
43
MRING
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
9
RRING
C1
1
2
0.01uF
R5
37.5
R6
37.5
1 T2 5
4
8
1:1
RTIP
RRING
The Transmit Section of the XRT74L73 contains a
block which is known as the Transmit DS3 LIU Inter-
face block. The purpose of the Transmit DS3 LIU In-
terface block is to take the outbound DS3 data
stream, from the Transmit DS3 Framer block, and to
do the following:
1. Encode this data into one of the following line
codes
a. Unipolar (e.g., Single-Rail)
b. AMI (Alternate Mark Inversion)
c. B3ZS (Bipolar 3 Zero Substitution)
225