XRT83VSH28IB-F View Datasheet(PDF) - Exar Corporation
Part Name
Description
MFG CO.
'XRT83VSH28IB-F' PDF : 74 Pages View PDF
PRELIMINARY
XRT83VSH28
REV. P1.0.0
8-CHANNEL E1 SHORT-HAUL LINE INTERFACE UNIT
2.0 RECEIVE PATH LINE INTERFACE
The receive path of the XRT83VSH28 LIU consists of 8 independent E1 receivers. The following section
describes the complete receive path from RTIP/RRING inputs to RCLK/RPOS/RNEG outputs. A simplified
block diagram of the receive path is shown in Figure 3.
FIGURE 3. SIMPLIFIED BLOCK DIAGRAM OF THE RECEIVE PATH
RCLK
RPOS
RNEG
HDB3 Decoder
Rx Jitter
Attenuator
Clock & Data
Recovery
Peak Detector
& Slicer
RTIP
RRING
2.1 Line Termination (RTIP/RRING)
2.1.1 CASE 1: Internal Termination
The input stage of the receive path accepts standard E1 twisted pair or E1 coaxial cable inputs through RTIP
and RRING. The physical interface is optimized by placing the terminating impedance inside the LIU. This
allows one bill of materials for all modes of operation reducing the number of external components necessary
in system design. The receive termination impedance is selected by programming TERSEL[1:0] to match the
line impedance. Selecting the internal impedance is shown in Table 2.
TABLE 2: SELECTING THE INTERNAL IMPEDANCE
TERSEL[1:0]
RECEIVE TERMINATION
0h (00)
Reserved
1h (01)
Reserved
2h (10)
75Ω
3h (11)
120Ω
The XRT83VSH28 has the ability to switch the internal termination to "High" impedance by programming
RxTSEL in the appropriate channel register. For internal termination, set RxTSEL to "1". By default, RxTSEL
is set to "0" ("High" impedance). For redundancy applications, a dedicated hardware pin (RxTSEL) is also
available to control the receive termination for all channels simultaneously. This hardware pin takes priority
over the register setting if RxTCNTL is set to "1" in the appropriate global register. If RxTCNTL is set to "0", the
state of this pin is ignored. See Figure 4 for a typical connection diagram using the internal termination.
FIGURE 4. TYPICAL CONNECTION DIAGRAM USING INTERNAL TERMINATION
XRT83VSH28 LIU
RTIP
Receiver
Input
RRING
Internal Impedance
1:1
Line Interface E1
One Bill of Materials
20
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