MC9S12NE64CPVE Datasheet, PDF (375/554 Pages) Freescale Semiconductor, Inc – MC9S12NE64 Device Overview

Functional Description
4B/5B Encoder/Decoder: The 4B/5B encoder converts the 4-bit nibbles from the reconciliation sublayer
to a 5-bit code group.
12.4.4.1.2 PMA Sublayer
The PMA provides medium-independent means for the PCS and other bit-oriented clients (e.g., repeaters)
to support the use of a range of physical media. For 100BASE-TX the PMA performs these functions:
• Mapping of transmit and receive code-bits between the PMA’s client and the underlying PMD
• Generating a control signal indicating the availability of the PMD to a PCS or other client
• Synchronization with the auto-negotiation function
• Generating indications of carrier activity and carrier errors from the PMD
• Recovery of clock from the NRZI data supplied by the PMD
12.4.4.1.3 PMD Sublayer
For 100BASE-TX, the ANSI X3.263: 199X (TP-PMD) standard is used. These signalling standards, called
PMD sublayers, define 125 Mbps, full-duplex signalling systems that use STP and UTP wiring.
Scrambler/De-scrambler: The scrambler and de-scrambler used in EPHY meet the ANSI Standard
X3.263-1995 FDDI TP-PMD. The purpose of the scrambler is to randomize the 125 Mbps data on
transmission resulting in a reduction of the peak amplitudes in the frequency spectrum. The de-scrambler
restores the received 5-bit code groups to their unscrambled values.
The scrambler input data (plaintext) is encoded by modulo 2 addition of a key stream to produce a
ciphertext bit stream. The key stream is a periodic sequence of 2047 bits generated by the recursive linear
function X[n] = X[n-11] + X[n-9] (modulo 2).
If not transmitting data, the scrambler encodes and transmits idles. This allows a pattern to use by the
de-scrambler to synchronize and decode the scrambled data.
The implementation of the scrambler and de-scrambler is as shown in Appendix G of the ANSI Standard
X3.263-1995.
For test, the scrambler can be bypassed by setting bit 18.5. Scrambler bypass mode is a special type of
interface for 100BASE-TX operation that bypasses the scrambler and de-scrambler operation. This mode
is typically used for test so that input and output test vectors match. In this mode, idles are not sent and the
MAC must provide idles.
MLT-3 Encoder/Decoder: An MLT-3 encoder is used in the transmit path to convert NRZ bit stream data
from the PMA sublayer into a three-level code. This encoding results in a reduction in the energy over the
critical frequency range. The MLT-3 decoder converts the received three-level code back to an NRZ bit
stream.
Baseline Wander: The use of the scrambler and MLT-3 encoding can cause long run lengths of 0s and 1s
that can produce a DC component. The DC component cannot be transmitted through the isolation
transformers and results in baseline wander. Baseline wander reduces noise immunity because the base
line moves nearer to either the positive or negative signal comparators. To correct for this EPHY uses DC
MC9S12NE64 Data Sheet, Rev. 1.1
Freescale Semiconductor
375