
XRT86L30
189
SINGLE T1/E1/J1 FRAMER/LIU COMBO
REV. 1.0.1
9.0
LIU RECEIVE PATH
9.1
Line Termination (RTIP/RRING)
9.1.1
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 impedance is selected by programming TERSEL[1:0] to
match the line impedance. Selecting the internal impedance is shown in Table 172.
The XRT86L30 has the ability to switch the internal termination to "High" impedance by programming RxTSEL
in the appropriate channel register, if the RxTSEL hardware pin is “High”. 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 available to control the receive termination for all channels simultaneously. This
hardware pin is AND-ed with the register bit. Both, the register bit and the hardware pin must be set active for
the receiver to be configured for internal impedance. Figure 57 shows a typical connection diagram using the
internal termination.
FIGURE 57. TYPICAL CONNECTION DIAGRAM USING INTERNAL TERMINATION
9.1.2
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 173.
TABLE 172: SELECTING THE INTERNAL IMPEDANCE
TERSEL[1:0]
RECEIVE TERMINATION
0h (00)
100
1h (01)
110
2h (10)
75
3h (11)
120
TABLE 173: SELECTING THE VALUE OF THE EXTERNAL FIXED
RESISTOR
RXRES[1:0]
EXTERNAL FIXED RESISTOR
0h (00)
None
1h (01)
240
2h (10)
210
3h (11)
150
R
TIP
R
RING
XRT86L30 LIU
1:1
Internal Impedance
Line Interface T1/E1/J1
One Bill of Materials
Receiver
Input
0.1
F