XRT83L314 Datasheet, PDF (20/84 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
2.1.2 CASE 2: Internal Termination With One External Fixed Resistor for All Modes
Along with the internal termination, a high precision external fixed resistor can be used to optimize the return
loss. This external resistor can be used for all modes of operation ensuring one bill of materials. There are
three resistor values that can be used by setting the RxRES[1:0] bits in the appropriate channel register.
Selecting the value for the external fixed resistor is shown in Table 3.
TABLE 3: SELECTING THE VALUE OF THE EXTERNAL FIXED RESISTOR
RXRES[1:0]
EXTERNAL FIXED RESISTOR
0h (00)
None
1h (01)
2h (10)
240Ω
210Ω
3h (11)
150Ω
By default, RxRES[1:0] is set to "None" for no external fixed resistor. If an external fixed resistor is used, the
XRT83L314 uses the parallel combination of the external fixed resistor and the internal termination as the input
impedance. See Figure 5 for a typical connection diagram using the external fixed resistor.
NOTE: Without the external resistor, the XRT83L314 meets all return loss specifications. This mode was created to add
flexibility for optimizing return loss by using a high precision external resistor.
FIGURE 5. TYPICAL CONNECTION DIAGRAM USING ONE EXTERNAL FIXED RESISTOR
XRT83L314 LIU
R_TIP
Receiver
Input
R_RING
Internal Impedance
1:1
R
Line Interface T1/E1/J1
R=240Ω, 210Ω, or 150Ω
16