Rainbow Electronics DS26519 - Manual (Page 97)

DS26519 16-Port T1/E1/J1 Transceiver
97 of 310
9.12.3 Receiver
9.12.3.1 Receive Internal Termination
The DS26519 contains 16 receivers. The termination circuit provides an analog switch that powers up in the open
setting, providing high impedance to the receive line side. This is useful for redundancy applications and hot
swapability.
Three termination methods are available:
• Partially internal impedance matching with a 120Ω external resistor, normally connected from RTIPEn to
RRINGn.
• External resistor termination, internal termination disabled.
See the LRISMR and LRCR registers for more details. Internal impedance match is configurable to 75
Ω, 100Ω,
110
Ω, or 120Ω termination by setting the appropriate RIMPM[1:0] bits. These bits must be configured to match line
impedance even if internal termination is disabled.
Table 9-41. Receive Impedance Control
LRISMR .
RIMPON
LRISMR .
REXTON
SETTING
0 0 Highimpedance.
0 1 Internal impedance disabled, RTIPEn connected to RTIPn.
1 0 Internal impedance enabled, RTIPEn disconnected from RTIPn.
1 1 Internal impedance enabled, RTIPEn connected to RTIPn.
Figure 9-23 shows a diagram of the switch control of termination. If internal impedance match is disabled, the
external resistor, R
T
, must match the line impedance.
Figure 9-23. Receive LIU Termination Options
RECEIVE LIU
RTIPn
RRINGn
1:1
TFR
Rx LINE
R
T
R R
RTIPEn
LRISMR.RIMPON
LRISMR.REXTON
The device couples to the receive E1 or T1 twisted pair (or coaxial cable in 75
Ω E1 applications) via a 1:1 or 2:1
transformer. See Table 9-40 for transformer details.
Receive sensitivity is configurable by setting the appropriate RSMS[1:0] bits ( LRCR ).