HBLXT9781HC.C4 Intel, HBLXT9781HC.C4 Datasheet - Page 36

• Manufacturer Part Number: HBLXT9781HC.C4
• Manufacturer: Intel

Specifications of HBLXT9781HC.C4

• Lead Free Status / RoHS Status: Not Compliant

LXT9761/9781 — Fast Ethernet 10/100 Multi-Port Transceiver with RMII
2.7.2.3
36
Carrier Sense/Data Valid
The LXT97x1 asserts CRS_DV whenever the respective port receiver is non-idle (as defined by
the RMII Specification Revision 1.2), including false carrier events. Assertion of CRS_DV is
asynchronous with respect to REFCLK. In the event that signal decoding is not complete when
CRS_DV is asserted, the LXT97x1 outputs 00 on the RXD1:0 lines until the decoded data is
available.
When the line returns to an idle state CRS_DV is de-asserted, asynchronously with respect to
REFCLK. In the event that the FIFO still contains data to be passed to the MAC via the RMII
when CRS is de-asserted, CRS_DV will toggle on nibble boundaries until the FIFO is empty. For
100BASE-X signals, CRS_DV toggles at 25 MHz. For 10BASE-T signals, CRS_DV toggles at
2.5 MHz.
Twisted-Pair PMD Sublayer
The twisted-pair Physical Medium Dependent (PMD) layer provides the signal scrambling and
descrambling, line coding and decoding (MLT-3 for 100TX, Manchester for 10T), as well as
receiving, polarity correction, and baseline wander correction functions.
Scrambler/Descrambler (100TX Only)
The purpose of the scrambler is to spread the signal power spectrum and further reduce EMI using
an 11-bit, non-data-dependent polynomial. The receiver automatically decodes the polynomial
whenever IDLE symbols are received.
The scrambler/descrambler can be bypassed by setting bit 16.12 = 1. The scrambler is
automatically bypassed when the fiber port is enabled. Scramber bypass is provided for diagnostic
and test support.
Baseline Wander Correction (100TX Only)
The LXT97x1 provides a baseline wander correction function which makes the device robust
under all network operating conditions. The MLT3 coding scheme used in 100BASE-TX is by
definition “unbalanced”. This means that the DC average value of the signal voltage can “wander”
significantly over short time intervals (tenths of seconds). This wander can cause receiver errors,
particularly in less robust designs, at long line lengths (100 meters). The exact characteristics of the
wander are completely data dependent.
The LXT97x1 baseline wander correction characteristics allow the device to recover error-free data
while receiving worst-case “killer” packets over all cable lengths.
Polarity Correction
The LXT97x1 automatically detects and corrects for the condition where the receive signal
(TPFIP/N) is inverted. Reversed polarity is detected if eight inverted link pulses, or four inverted
End-of-Frame (EOF) markers, are received consecutively. If link pulses or data are not received
by the maximum receive time-out period, the polarity state is reset to a non-inverted state.
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