XRT83L314 Datasheet, PDF (19/84 Pages) Exar Corporation – 14-CHANNEL T1/E1/J1 LONG-HAUL/SHORT-HAUL LINE INTERFACE UNIT

XRT83L314
14-CHANNEL T1/E1/J1 LONG-HAUL/SHORT-HAUL LINE INTERFACE UNIT
REV. 1.0.0
2.1 Line Termination (RTIP/RRING)
2.1.1 CASE 1: Internal Termination
The input stage of the receive path accepts standard T1/E1/J1 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 (along with the transmit 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)
100Ω
1h (01)
2h (10)
110Ω
75Ω
3h (11)
120Ω
The XRT83L314 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
XRT83L314 LIU
R_TIP
Receiver
Input
R_RING
Internal Impedance
1:1
Line Interface T1/E1/J1
One Bill of Materials
15