XRT82D20_06 Datasheet, PDF (24/27 Pages) Exar Corporation – SINGLE CHANNEL E1 LINE INTERFACE UNIT

XRT82D20
SINGLE CHANNEL E1 LINE INTERFACE UNIT
REV. 1.0.8
2.0 DIAGNOSTIC FEATURES
In order to support diagnostic operations, the XRT82D20 supports the following loop-back modes:
• Local Loopback
• Remote Loopback
• Digital Loopback
Each of these loop-back modes will be discussed below.
2.1 The Local Loop-Back Mode
When the XRT82D20 is configured to operate in the Local Loop-Back Mode, the XRT82D20 will ignore any
signals that are input to the RTIP and RRing input pins. The Transmitting Terminal Equipment will transmit
data into the XRT82D20 via the TPOS, TNEG and TClk input pins. This data will be processed through the
Transmit Terminal Input Interface and the Pulse Shaping circuit. Finally, this data will be output to the line via
the TTIP and TRing output pins. Additionally, this data (which is being output via the TTIP and TRing output
pins) will be looped back into the Receiver block. As a consequence, this data will also be processed through
the entire Receive Section of the XRT82D20. After this post-loop-back data has been processed through the
Receive Section it will output, to the Near-End Receiving Terminal Equipment via the RPOS and RNEG output
pins.
Figure 18, illustrates the path that the data takes (within the XRT82D20), when the chip is configured to
operate in the Local Loop-Back Mode.
The user can configure the XRT82D20 to operate in the Local Loop-Back Mode, by pulling the LLoop input pin
(pin 9) to GND.
FIGURE 18. ILLUSTRATION OF THE ANALOG LOCAL LOOP-BACK WITHIN THE XRT82D20
TClk
TPOS
TNEG
HDB3
Encoder
MUX
RClk
RPOS
RNEG
HDB3
Decoder
MUX
Tx Pulse
Shaper
Line
Driver
Jitter Attenuator
Data &
Timing
Recovery
LOS
Detect
Data
Slicer
Local
Loopback
Peak
Detector
Timing
Generator
TTIP
TRing
RLOS
RTIP
RRing
MClk
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