TLK4015 Datasheet, PDF (11/24 Pages) Texas Instruments – QUAD 0.6 TO 1.5 Gbps TRANSCEIVER

TLK4015
QUAD 0.6 to 1.5 Gbps TRANSCEIVER
SLLS541 – DECEMBER 2002
detailed description (continued)
serial-to-parallel
Serial data is received on the DINRxP and DINRxN terminals. The interpolator and clock recovery circuit locks
to the data stream if the clock to be recovered is within 200 PPM of the internally generated bit-rate clock. The
recovered clock is used to retime the input data stream. The serial data is then clocked into the serial-to-parallel
shift registers. The 10-bit-wide parallel data is then multiplexed and fed into two separate 8-bit/10-bit decoders,
where the data is synchronized to the incoming data-stream word boundary by detection of the K28.5
synchronization pattern.
comma detect and 8-bit/10-bit decoding
The TLK4015 has two parallel 8-bit/10-bit decode circuits. Each 8-bit/10-bit decoder converts 10-bit encoded
data (half of the 20-bit received word) back into 8 bits. The comma detect circuit is designed to provide for byte
synchronization to an 8-bit/10-bit transmission code. When parallel data is clocked into a parallel-to-serial
converter, the byte boundary that was associated with the parallel data is now lost in the serialization of the data.
When the serial data is received and converted to parallel format again, a way is needed to recognize the byte
boundary. This is accomplished through the use of a synchronization pattern. This is generally a unique pattern
of 1s and 0s that either cannot occur as part of valid data or is a pattern that repeats at defined intervals.
8-bit/10-bit encoding contains a character called the comma (0011111b or 1100000b), which is used by the
comma detect circuit on the TLK4015 to align the received serial data back to its original byte boundary. The
decoder detects the K28.5 comma, generating a synchronization signal aligning the data to their 10-bit
boundaries for decoding. It then converts the data back into 8-bit data, removing the control words. The output
from the two decoders is latched into the 16-bit register synchronized to the recovered parallel data clock
(Rx_CLK), and the output is valid on the rising edge of the Rx_CLK.
It is possible for a single bit error in a data pattern to be interpreted as comma on an erroneous boundary. If the
erroneous comma is taken as the new byte boundary, all subsequent data is improperly decoded until a property
aligned comma is detected. To prevent a data bit error from causing a valid data packet to be interpreted as a
comma and thus cause the erroneous word alignment by the comma detection circuit, the comma word
alignment circuit is turned off when a properly aligned comma has been received after the link is established.
The link is established after three idle patterns or one valid data pattern is properly received. The comma
alignment circuit is re-enabled when the synchronization state machine detects a loss of synchronization
condition (see synchronization and initialization).
Two output signals, Rx_DV/LOSx and Rx_ER, are generated along with the decoded 16-bit data output on the
RDx[0–15] terminals. The receive status signals are asserted as shown in Table 2. When the TLK4015 decodes
normal data and outputs the data on RDx[0–15], Rx_DV/LOSx is asserted (logic high) and Rx_ER is deasserted
(logic low). When the TLK4015 decodes a K23.7 code (F7F7) indicating carrier extend, Rx_DV/LOSx is
deasserted and Rx_ER is asserted. If the decoded data is not a valid 8-bit/10-bit code, an error is reported by
the assertion of both Rx_DV/LOSx and Rx_ER. If the error was due to an error propagation code, the RDx bits
output hex FEFE. If the error was due to an invalid pattern, the data output on RDx is undefined. When the
TLK4015 decodes an IDLE code, both Rx_DV/LOSx and Rx_ER are deasserted and a K28.5 (BC) code
followed by either a D5.6 (C5) or D16.2 (50) code are output on the RDx terminals.
Table 2. Receive Status Signals
ENCODED 20-BIT OUTPUT
IDLE (<K28.5, D5.6>, <K28.5, D16.2>)
Carrier extend (K23.7, K23.7)
Normal data character (DX.Y)
Transmit error propagation (K30.7, K30.7)
Rx_DV/LOSx
0
0
1
1
Rx_ER
0
1
0
1
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