Intel PCI-X manual 11.12 100 Mbps Operation, 11.13 10 Mbps Operation, Descrambler

PHY Functionality and Features

•Far-end crosstalk (FEXT)

•Propagation delay variations between channels of up to 120 ns.

•Extraneous tones that have been coupled into the receive path.

The adaptive filter coefficients are initially set during the training phase. They are continuously adjusted (adaptive equalization) during operation through the decision-feedback loop.

11.11.4.6Descrambler

The descrambler identifies each channel by its characteristic signature, removing the signature and re-routing the channel internally. In this way, the receiver can correct for channel swaps and polarity reversals. The descrambler uses the same base LFSR used by the transmitter on the other side of the link.

The descrambler requires approximately 15 ∝s. to lock, normally accomplished during the training phase.

11.11.4.7Viterbi Decoder/Decision Feedback Equalizer (DFE)

The Viterbi decoder generates clean 4DPAM5 symbols from the output of the DSP. The decoder includes a Trellis encoder identical to the one used by the transmitter. The Viterbi decoder simulta- neously looks at the received data over several baud periods. For each baud period, it predicts whether the symbol received should be even or odd, and compares that to the actual symbol received. The 4DPAM5 code is organized in such a way that a single level error on any channel changes an even code to an odd one and vice versa. In this way, the Viterbi decoder can detect single-level coding errors, effectively improving the Signal-To-Noise (SNR). When an error occurs, this information is quickly fed back into the equalizer to prevent future errors.

11.11.4.84DPAM5 Decoder

The 4DPAM5 decoder generates 8B data from the output of the Viterbi decoder.

11.12100 Mbps Operation

The MAC passes data to the PHY over the MII. The PHY encodes and scrambles the data, then transmits it using MLT-3 for 100TX over copper. The PHY descrambles and decodes MLT-3 data received from the network. When the MAC is not actively transmitting data, the PHY sends out idle symbols on the line.

11.1310 Mbps Operation

The PHY operates as a standard 10 Mbps transceiver. Data transmitted by the MAC as 4-bit nibbles is serialized, Manchester-encoded, and transmitted on the MDI[0]+/- outputs. Received data is decoded, de-serialized into 4-bit nibbles and passed to the MAC across the internal MII. The PHY supports all the standard 10 Mbps functions.

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