XRT74L73 Datasheet, PDF (327/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

PRELIMINARY
XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
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).
NOTE: This register is only active if the XRT74L73 Framer
IC has been configured to insert the BIP-4 nibble into each
outbound E3 frame.
TXE3 BIP-4 ERROR MASK REGISTER (ADDRESS = 0X4A)
BIT 7
R/W
0
BIT 6
BIT 5
Not Used
R/W
R/W
0
0
BIT 4
R/W
0
BIT 3
R/W
0
BIT 2
BIT 1
TxBIP-4 Mask[2:0]
R/W
R/W
0
0
BIT 0
R/W
0
5.2.5 The Transmit E3 Line Interface Block
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.
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).
FIGURE 127. APPROACH TO INTERFACING THE XRT74L73 FRAMER IC TO THE XRT73L00 DS3/E3/STS-1 LIU
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
61
TxSER
TxInClk
TxFrame
25 _NIBBLEINTF
28 _RESETB
13
8
7
10
9
6
INTB
CSB
WRB_RW
RDB_DS
ALE_AS
Rdy_Dtck
15
16
17
18
19
A0
A1
A2
A3
20
21
22
23
A4
A5
A6
A7
A8
32
33
34
35
36
37
38
39
D0
D1
D2
D3
D4
D5
D6
D7
27
MOTO
86
88
90
RxSer
RxClk
RxFrame
95
94
93
RxLOS
RxOOF
87
RxRED
RxAIS
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
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
TRING ⁴⁰
MTIP ⁴⁴
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
RTIP ⁸
RRING ⁹
C1
12
0.01uF
R5
37.5
R6
37.5
1 ^T2 5
4
8
1:1
RTIP
RRING
328