XRT82D20_06 Datasheet, PDF (25/27 Pages) Exar Corporation – SINGLE CHANNEL E1 LINE INTERFACE UNIT

XRT82D20
REV. 1.0.8
SINGLE CHANNEL E1 LINE INTERFACE UNIT
2.2 The Remote Loop Back Mode
When the XRT82D20 is configured to operate in the Remote Loop-Back Mode, the XRT82D20 will ignore any
signals that are input to the TPOS and TNEG input pins. The XRT82D20 will receive the incoming line signals,
via the RTIP and RRing input pins. This data will be processed through the entire Receive Section (within the
XRT82D20) and will output to the Receive Terminal Equipment via the RPOS and RNEG output pins.
Additionally, this data will also be internally looped back to the Transmit Input Interface block within the
Transmit Section. At this point, this data will be routed through the remainder of the Transmit Section of the
XRT82D20 and will be transmitted out onto the line via the TTIP and TRing output pins.
Figure 19, illustrates the path that the data takes (within the XRT82D20) when the chip is configured to
operate in the Remote Loop-Back Mode.
FIGURE 19. ILLUSTRATION OF THE REMOTE LOOP-BACK PATH, WITHIN THE XRT82D20
TClk
TPOS
TNEG
RClk
RPOS
RNEG
HDB3
Encoder
MUX
Remote
Loopback
HDB3
Decoder
MUX
Tx Pulse
Shaper
Line
Driver
Jitter Attenuator
Data &
Timing
Recovery
LOS
Detect
Data
Slicer
Peak
Detector
Timing
Generator
TTIP
TRing
RLOS
RTIP
RRing
MClk
NOTE: During Remote Loop-Back operation, any data which is input via the RTIP and RRING input pins, will also be output
to the Terminal Equipment, via the RPOS and RNEG output pins.
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