XRT4500 Datasheet, PDF (60/99 Pages) Exar Corporation – MULTIPROTOCOL SERIAL NETWORK INTERFACE IC

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XRT4500
MULTIPROTOCOL SERIAL NETWORK INTERFACE IC
REV. 1.0.7
the SCTE clock signal; it is highly unlikely that the
“DCE Equipment” manufacturer will be able to (over
the DTE/DCE Interface) invoke the “Echo-Clock”
mode and resolve the “2-Clock/Propagation Delay”
phenomenon.
NOTE: This is especially the case if the DTE Equipment is
not using the XRT4500 as the Multi-protocol Transceiver IC.
As a consequence, the “DCE Equipment” manufac-
turer would have to resort to undesirable things, such
as using the (locally generated) TXC signal as the
sampling clock for the “TXD” signal.
However, the XRT4500 does offer the DCE Equip-
ment manufacturer an elegant solution to the “2-
Clock/Propagation Delay” phenomenon. By doing the
following things.
a. Configuring the DCE Mode XRT4500 to operate in
the “2-Clock” Mode, and
b. Inverting the TXC signal, within the DCE Mode
XRT4500, the user can largely resolve the “2-Clock/
Propagation Delay” phenomenon.
Figure 30 presents an illustration of the DCE Mode
XRT4500, being configured to (1) operate in the “2-
Clock” Mode, and (2) to invert the “TXC” signal.
FIGURE 30. ILLUSTRATION OF THE DCE MODE XRT4500, WHICH IS OPERATING IN THE “2-CLOCK” MODE, AND
INVERTING THE “TXC” SIGNAL
SCC (L)
TXD
SCTE
DTE
60
TX1
67
TX2
63
TXD
78
62
79
64
SCTE
77
65
76
DCE
RX1
RX2
SCC (R)
1
TXD_IN
74
SCTE_IN
TXC_IN
RXC_IN
RXD_IN
70
TXC
70
73
RX3
71
71
77
RXC
64
74
RX2
76
65
78
RXD
63
1
RX1
79
62
XRT4500
TX3
TX2
TX1
XRT4500
68
TXC
67
RXC
60
RXD_OUT
By taking advantage of both the “2-Clock” Mode and
the ability to invert the “TXC” clock signal, the “DCE
Equipment” manufacture can mitigate the “2-Clock/
Propagation Delay” phenomenon by simply inverting
the “TXC” whenever the DTE/DCE Interface and sys-
tem configuration settings begin to violate the “TXD to
TXC” set-up time requirement of the DCE SCC de-
vice. By inverting the TXC signal, the phase relation-
ship, between the “TXD and the TXC signal will shift
by 180 degrees. At this point, the sampling edge of
the TXC signal will be near the middle of the “TXD”
bit-period, and the system will not be violating the
“TXD to TXC” set-up time requirements of the DCE
SCC device.
In summary, the “2-Clock” Mode (within the
XRT4500) provides the user with the following op-
tions.
The DCE Equipment (which uses the XRT4500) can
easily be configured to interface to DTE Equipment
that supports the SCTE clock signal, as well as DTE
Equipment that does not support the SCTE clock sig-
nal. If the DCE Equipment is being interfaced to a
DTE which supports the SCTE clock signal, then the
DCE Equipment should configure the XRT4500 to op-
erate in the “3-Clock” Mode. Conversely, if the DCE
Equipment is being interfaced to a DTE which does
not support the SCTE clock signal, then the DCE
Equipment should configure the XRT4500 to operate
in the “2-Clock” Mode. This step will automatically
configure the XRT4500 to route the “TXC” clock sig-
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