XRT74L74
4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
ADVANCED CONFIDENTIAL
REV. P1.1.1
236
The XRT74L74 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 XRT74L74 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).
The Transmit Section of the XRT74L74 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)
2.
And to transmit this data to the LIU IC.
Figure 73 presents a simple illustration of the Trans-
mit DS3 LIU Interface block.
F
IGURE
72. A
PPROACH
TO
I
NTERFACING
THE
XRT74L74 F
RAMER
IC
TO
THE
XRT73L00 DS3/E3/STS-1 T
RANS
-
MITTER
LIU (
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
RDB_DS
ALE_AS
7
10
9
CSB
8
INTB
13
TxSER
TxInClk
TxFrame
46
43
61
RxSer
RxClk
RxFrame
86
88
90
RxLOS
RxOOF
RxRED
RxAIS
95
94
93
87
NIBBLEINTF
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
INTB
RxSer
RxClk
RxFrame
RxLOS
RxOOF
RxRED
RxAIS
A[8:0]
TRING
TTIP
INTB
D[7:0]