XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
PRELIMINARY
REV. P1.0.1
328
As the Transmit E3 Framer block formulates the out-
bound E3 frames, the contents of the BIP-4 bits are
automatically XORed with the contents of this regis-
ter. The results of this XOR operation is written back
into the corresponding bit-field within the outbound
E3 frame, and is transmitted to the Remote Terminal
Equipment. Therefore, if the user does not wish to
modify any of these bits, then this register must con-
tain all “0’s” (the default value).
N
OTE
:
This register is only active if the XRT74L73 Framer
IC has been configured to insert the BIP-4 nibble into each
outbound E3 frame.
5.2.5
The XRT74L73 Framer IC is a digital device that
takes E3 payload and overhead bit information from
some terminal equipment, processes this data and ul-
timately, multiplexes this information into a series of
outbound E3 frames. However, the XRT74L73 Fram-
er IC lacks the current drive capability to be able to di-
rectly transmit this E3 data stream through some
transformer-coupled coax cable with enough signal
strength for it to be received by the remote receiver.
The Transmit E3 Line Interface Block
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 be reli-
ably received by the far-end receiver. Figure 127
presents a circuit drawing depicting the Framer IC in-
terfacing to an LIU (XRT73L00 DS3/E3/STS-1 Trans-
mit LIU).
TXE3 BIP-4 ERROR MASK REGISTER (ADDRESS = 0X4A)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Not Used
TxBIP-4 Mask[2:0]
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
0
0
0
0
0
0
0
0
F
IGURE
127. A
PPROACH
TO
I
NTERFACING
THE
XRT74L73 F
RAMER
IC
TO
THE
XRT73L00 DS3/E3/STS-1 LIU
5V
U1
XRT74L74
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
6
WRB_RW
7
10
9
8
CSB
13
TxSER
TxFrame
46
43
61
RxSer
86
88
90
RxLOS
RxRED
RxAIS
95
94
93
87
NIBBLEINTF
25
U2
XRT73L00
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
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]