TLK2701 Datasheet, PDF (9/21 Pages) Texas Instruments – 1.6 TO 2.7 GBPS TRANSCEIVER

TLK2701
1.6 TO 2.7 GBPS TRANSCEIVER
SLLS429B – AUGUST 2000 – REVISED MAY 2002
detailed description (continued)
comma detect and 8-bit/10-bit decoding
The TLK2701 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. Generally 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. 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 TLK2701 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. It 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 (RX_CLK) and output valid on
the rising edge of the RX_CLK.
NOTE:
The TLK2701 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 was received and the specific K code is presented on the data bits RXD0 – RXD7, else an 8-bit/10-bit
D code was received. When TKMSB is asserted, an 8-bit/10-bit K code was received and the specific K code
is presented on data bits RXD8 – RXD15, else an 8-bit/10-bit D code was received. The valid K codes the
TLK2701 will decode are provided in Table 3. An error detected on either byte, including K codes not in Table
3, will cause that byte only to indicate a K0.0 code on the RK×SB and associated data pins, where K0.0 is known
to be an invalid 8-bit/10-bit code. A loss of input signal will cause 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
Table 2. Receive Status Signals
RKMSB
0
1
0
1
DECODED 20 BIT OUTPUT
Valid data on RXD(0–7), Valid data RXD(8–15)
Valid data on RXD(0–7), K code on RXD(8–15)
K code on RXD(0–7), Valid data on RXD(8–15)
K code on RXD(0–7), K code on RXD(8–15)
Table 3. Valid K Characters
K CHARACTER
K28.0
K28.1
K28.2
K28.3
K28.4
K28.5
K28.6
K28.7
K23.7
K27.7
K29.7
K30.7
RECEIVE DATA BUS
(RXD[7–0]) OR
(RXD[15–8])
000 11100
001 11100
010 11100
011 11100
100 11100
101 11100
110 11100
111 11100
111 10111
111 11011
111 11101
111 11110
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