XRT83SL28 View Datasheet(PDF) - Exar Corporation
Part Name
Description
MFG CO.
'XRT83SL28' PDF : 47 Pages View PDF
xr
REV. 1.0.0
XRT83SL28
8-CHANNEL E1 SHORT-HAUL LINE INTERFACE UNIT
3.2.3 Receive Interface with 1:1 and 1+1 Redundancy
The receivers on the backup card should be programmed for "High" impedance. Since there is no external
resistor in the circuit, the receivers on the backup card will not load down the line interface. This key design
feature eliminates the need for relays and provides one bill of materials for all interface modes of operation.
Select the impedance for the desired mode of operation, E1 75Ω or 120Ω. To swap the primary card, set the
backup card to internal impedance, then the primary card to "High" impedance. See Figure 22. for a simplified
block diagram of the receive section for a 1:1 redundancy scheme.
FIGURE 22. SIMPLIFIED BLOCK DIAGRAM OF THE RECEIVE INTERFACE FOR 1:1 AND 1+1 REDUNDANCY
Backplane Interface
Primary Card
Rx
Internal Impedance
Backup Card
Rx
"High" Impedance
XRT83SL28
1:1
XRT83SL28
1:1
E1 Line
3.2.4 N+1 Redundancy Using External Relays
N+1 redundancy has one backup card for N primary cards. Due to impedance mismatch and signal
contention, external relays are necessary when using this redundancy scheme. The relays create complete
isolation between the primary cards and the backup card. This allows all transmitters and receivers on the
primary cards to be configured in internal impedance, providing one bill of materials for all interface modes of
operation. The transmit and receive sections of the LIU device are described separately.
27
Share Link: 
