XRT4500CV View Datasheet(PDF) - Exar Corporation
Part Name
Description
MFG CO.
'XRT4500CV' PDF : 96 Pages View PDF
áç
XRT4500
MULTIPROTOCOL SERIAL NETWORK INTERFACE IC
REV. 1.0.5
2. The Analog/Line-Side Loop-back path:
This loop-back path is referred to as an “Analog/Line-
Side” Loop-back, because all signals originate from and
are ultimately terminated by the DCE Terminal. These
signals originate from the DCE Terminal; and are out-
putted to the line, to the DTE Terminal. However, these
signals (from the DCE Terminal) are never converted in-
to the Digital format (by the DTE Mode XRT4500).
These signal are kept in the “Analog” format, and are
looped-back (over the line) to the DCE Terminal.
The RXD signal (originating from the DCE Terminal)
will be transmitted over the line to the DTE Terminal.
However, this signal will not be converted into the dig-
ital format by the “DTE Mode” XRT4500. Instead, this
signal will be looped-back out to the “DCE Terminal”
via the “TXD” signal path.
NOTE: In this loop-back mode, the RXC signal (e.g., the
companion clock signal to RXD) is also received by the
DTE Terminal and looped-back out to the DCE Terminal. In
this case, the “RXC” (Receive Clock) signal will be routed to
the DCE Terminal through the “SCTE” signal path The DCE
SCC can still use the RXC (via the SCTE signal path), in
order to sample the RXD signal (which is available via the
“TXD” signal path).
Behavior of the DCE Mode XRT4500, when the
Loop-Back Mode is Enabled.
Figure 19 presents an illustration of a DTE and a
DCE Terminal interfaced to each other. In this case,
the XRT4500 (associated with the DCE Terminal) has
been configured to operate in the “Loop-back” Mode.
FIGURE 19. ILLUSTRATION OF THE BEHAVIOR OF THE DCE MODE XRT4500, WHEN IT IS CONFIGURED TO OPERATE
IN THE LOOP-BACK MODE
SCC (L)
TXD
SCTE
TXC_IN
RXC_IN
RXD_IN
DTE (#1)
60
TX1
63 TXD 78
62
79
67
TX2
64 SCTE 77
65
76
73
RX3
74
RX2
1
RX1
XRT4500
70 TXC 70
71
71
77 RXC 64
76
65
78 RXD 63
79
62
Analog/Line
Loop-back Path
DCE (#4)
MUX 1
RX1
Digital/Terminal
Loop-back Path
SCC (R)
1
TXD_IN
74
RX2
SCTE_IN
TX3
TX2
TX1
XRT4500
68
TXC
67
RXC
60
RXD
NOTE: Figure 19 only depicts the “High-Speed” DCE/DTE
Interface signals. The “Low-Speed” control/handshaking
signals are not affected by the loop-back mode.
If the Loop-back Mode is configured within the
XRT4500, while it is operating in the DCE Mode, then
the following two (2) loop-back paths exists.
• A Digital/Terminal-Side Loop-back
• An Analog/Line-Side Loop-back
Each of these Loop-back paths are described below.
1. The Digital/Terminal Side Loop-back:
Again, this loop-back path is referred to as a “Digital/
Terminal Side” Loop-back, because all of the signals
originate from, and are terminated by the DCE SCC
(e.g., the Terminal Equipment). The signals (originat-
ing at the DCE SCC) are not converted into the Ana-
log format, and are not output to the line.
The “RXD” signal (originating from the DCE SCC)
along with the “RXC” (Receive Clock) signal will not
be converted into the Analog format, nor output to the
DTE Terminal (over the line). Instead, this signal will
remain in the “Digital-format” and will be looped-back
into the DCE SCC. The “RXD” signal will ultimately be
output to the DCE SCC via the “TXD” output of the
“DCE Mode” XRT4500.
NOTE: The “RXC” signal (e.g., the companion clock signal to
“RXD”) will also be loop-back into the “DCE SCC”. This signal
will be output (by the XRT4500) via the “SCTE” output pin.
48
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