MC92052 Datasheet, PDF (2/6 Pages) Motorola, Inc – FTTC User Framer

General Description
The MC92052 implements the TC sublayer of the DAV-
IC asymmetrical FTTC PHY specification for user devic-
es. The MC92052 key functional blocks are described in
the paragraphs which follow.
Rx PMD Interface
The receive PMD interface receives a clock signal and
a serial data stream. The clock is used both to sample
the data and to clock the operation of the MC92052.
Frame Alignment
When in the “out-of-frame” condition, the frame align-
ment block searches the serial data (which is LSB first)
for the 16-bit framing pattern and then converts it to 8-
bit parallel data aligned to the framing pattern. When in
the “in-frame” condition, the serial-to-parallel block ver-
ifies the framing pattern and continues to convert it to
parallel data using the current alignment. In each frame,
the two framing bytes are discarded, the next 16 bytes
are provided to the header flow, and the following
(12 * 66) bytes are provided to the payload flow.
Deinterleaver
The deinterleaver block recovers the original data
blocks from the interleaved data that it receives. Trans-
mitting interleaved data allows for better correction of
bursts of errors because the deinterleaver spreads the
incorrect data over many blocks so that the Reed-So-
lomon decoder can correct the small number of errors
in each block.
The deinterleaver separates the data byte stream into
33 branches. Each of the branches is delayed by a dif-
ferent amount, and then they are recombined into a sin-
gle data stream. The delay of branch k (0 ≤ k ≤ 32) is
M * (32 - k). M is the Interleaving Depth Parameter re-
covered from the frame header and ranges from 0 to 31.
M=0 effectively disables the deinterleaver.
The delay of the interleaver/deinterleaver combination
is 1056 * M payload byte periods. The deinterleaver is
implemented using an external SRAM (Motorola
MCM6306 or equivalent). Alternatively, the internal
RAM can be used if the value of M is 1 or 2.
Reed-Solomon Decoders
One Reed-Solomon decoder is used for the header. It
decodes the (16,12) code in order to correct up to 2
bytes or declare the header to be uncorrectable.
The other decoder is used for the payload blocks. It de-
codes the (66,58) codes in order to correct up to 4 bytes
or declare the block to be uncorrectable, in which case
the data is not touched.
Derandomizers
The received data has been randomized on the network
side for better transmission performance. The deran-
domizers perform the inverse function to restore the
original data.
The two derandomizers are identical. One is used for
the 12 header bytes per frame, and the other is used for
the 12*58 payload bytes per frame. The derandomizers
are self-synchronizing since they depend only on the
previously received data.
Frame Header Interpretation Block
The header interpretation block extracts the useful in-
formation from the received frame header. It provides
information to the transmit flow regarding when to
transmit a cell, etc.
Data Link Extraction
The data link extraction block optionally provides the
data link bytes of the downstream frame headers to a
serial data link controller (e.g., MC68360 QUICC) for
further processing. The received downstream data link
bytes are extracted using a clock pin and a data pin.
Rx Cell Functions
The receive cell functions block recovers 53-octet ATM
cells from the derandomized byte stream using the
HEC-based method described in ITU-T Recommenda-
tion I.432.
Once the cell alignment has been recovered, the re-
ceive cell functions block checks the received HEC val-
ue against the calculated value and corrects single-bit
errors in the header. Any cell with non-correctable er-
rors is discarded. Then the cells are filtered based on
the header value. Idle cells are discarded. Additional
cells may be discarded as a result of the GFC/VPI pat-
tern matching option.
The cell functions block also derandomizes the payload
of the ATM cells to recover the original data and trans-
fers entire ATM cells to the receive cell FIFO.
Counts of the cells transferred to the receive cell FIFO
and the cells that are discarded due to header errors are
maintained.
Rx UTOPIA Interface
The receive UTOPIA interface reads the ATM cells from
the receive cell FIFO and transfers them to the ATM lay-
er according to the ATM Forum UTOPIA Level 1 speci-
Motorola
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MC92052