TLK2711-SP_15 Datasheet, PDF (17/29 Pages) Texas Instruments – 1.6-Gbps to 2.5-Gbps Class V Transceiver

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TLK2711-SP
SGLS307N – JULY 2006 – REVISED DECEMBER 2015
8.3.12 Comma Detect and 8-Bit/10-Bit Decoding
The TLK2711-SP 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 method is needed to recognize the
byte boundary. Typically, this is accomplished through the use of a synchronization pattern. This is typically 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. The 8-bit/10-bit encoding contains a character called the comma (b0011111 or b1100000), which is
used by the comma-detect circuit on the TLK2711-SP to align the received serial data back to its original byte
boundary. The decoder detects the comma, generating a synchronization signal aligning the data to their 10-bit
boundaries for decoding; the comma is mapped into the LSB. The decoder then converts the data back into 8-bit
data. The output from the two decoders is latched into the 16-bit register synchronized to the recovered parallel
data clock (RXCLK) and output valid on the rising edge of the RXCLK.
NOTE
The TLK2711-SP only achieves byte alignment on the 0011111 comma.
Decoding provides two additional status signals, RKLSB and RKMSB. When RKLSB is asserted, an 8-bit/10-bit
K code is received and the specific K code is presented on the data bits RXD0 to RXD7; otherwise, an 8-bit/10-
bit D code is received. When RKMSB is asserted, an 8-bit/10-bit K code is received and the specific K-code is
presented on data bits RXD8 to RXD15; otherwise, an 8-bit/10-bit D code is received (see Table 3). The valid K
codes the TLK2711-SP; decodes are provided in Table 4. An error detected on either byte, including K codes not
in Table 4, causes that byte only to indicate a K0.0 code on the RKxSB and associated data pins, where K0.0 is
known to be an invalid 8-bit/10-bit code. A loss of input signal causes a K31.7 code to be presented on both
bytes, where K31.7 is also known to be an invalid 8-bit/10-bit code.
RKLSB
0
0
1
1
RKMSB
0
1
0
1
Table 3. Receive Status Signals
DECODED 20-BIT OUTPUT
Valid data on RXD0 to RXD7 Valid data RXD8 to RXD15
Valid data on RXD0 to RXD7 K code on RXD8 to RXD15
K code on RXD0 to RXD7
Valid data on RXD8 to RXD15
K code on RXD0 to RXD7
K code on RXD8 to RXD15
Table 4. Valid K Characters
K CHARACTER
K28.0
K28.1 ⁽¹⁾
K28.2
K28.3
K28.4
K28.5 ⁽¹⁾
K28.6
K28.7 ⁽¹⁾
K23.7
K27.7
K29.7
K30.7
RECEIVE DATA BUS
RXD0 to RXD7 OR RXD8 to RXD15
000 11100
001 11100
010 11100
011 11100
100 11100
101 11100
110 11100
111 11100
111 10111
111 11011
111 11101
111 11110
(1) Should only be present on RXD0 to RXD7 when in running disparity
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