CRD8900-1 View Datasheet(PDF) - Cirrus Logic
Part Name
Description
MFG CO.
CRD8900-1 Datasheet PDF : 132 Pages
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CS8900
LinkOK
(to MAC)
ENDEC
RXSQL
RX
TX
10BASE-T Transceiver
Link Pulse
Detector
RX Squelch
RX
Comparator
RX Filters
TX Pre-
Distortion
TX Filters
Filter Tuning
TX Drivers
RXD-
RXD+
TXD-
TXD+
Figure 3.10. 10BASE-T Transceiver
Transmitter
When configured for 10BASE-T operation, Man-
chester encoded data from the ENDEC is fed
into the transmitter’s pre-distortion circuit where
initial wave shaping and pre-equalization is per-
formed. The output of the pre-distortion circuit is
fed into the transmit filter where final wave
shaping occurs and unwanted noise is removed.
The signal then passes to the differential driver
where it is amplified and driven out of the
TXD+/TXD- pins.
In the absence of transmit packets, the transmit-
ter generates link pulses in accordance with
section 14.2.1.1. of the Ethernet standard. Trans-
mitted link pulses are positive pulses, one bit
time wide, typically generated at a rate of one
every 16 ms. The 16 ms timer starts whenever
the transmitter completes an End-of-Frame
(EOF) sequence. Thus, there is a link pulse 16
ms after an EOF unless there is another transmit-
ted packet. Figure 3.11 diagrams the operation of
the Link Pulse Generator.
If no link pulses are being received on the re-
ceiver, the 10BASE-T transmitter is internally
forced to an inactive state unless bit DisableLT
in register 19 (Test Control register) is set to one.
Receiver
The 10BASE-T receive section consists of the
receive filter, squelch circuit, polarity detection
and correction circuit, and link pulse detector.
Squelch Circuit: The 10BASE-T squelch circuit
determines when valid data is present on the
RXD+/RXD- pair. Incoming signals passing
through the receive filter are tested by the
squelch circuit. Any signal with amplitude less
than the squelch threshold (either positive or
negative, depending on polarity) is rejected.
32
DS150PP2
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