TLK1221 Datasheet, PDF (4/23 Pages) Texas Instruments – ETHERNET TRANSCEIVER

TLK1221
SLLS713 – FEBRUARY 2007
www.ti.com
RBC0
RBC1
SYNC
RD(0–9)
t_d(S)
t_d(S)
t_d(H)
t_d(H)
K28.5
DXX.X
DXX.X
DXX.X
K28.5
DXX.X
Figure 2. Synchronous Timing Characteristic Waveforms (TBI Half-Rate Mode)
The receiver clock interpolator can lock to the incoming data without the need for a lock-to-reference preset. The
received serial data rate (RXP and RXN) is at the same baud rate as the transmitted data stream, ±0.02% (200
PPM) for proper operation.
RBC0
SYNC
t_d(S)
t_d(H)
RD(0–9)
K28.5
DXX.X
DXX.X
DXX.X
K28.5
DXX.X
Figure 3. Synchronous Timing Characteristic Waveforms (TBI Full-Rate Mode)
Receiver Word Alignment
These devices use the IEEE 802.3 Gigabit Ethernet defined 10-bit K28.5 character, which contains the 7-bit
comma-pattern word alignment scheme. The following sections explain how this scheme works and how it
realigns to the proper byte boundary of the data.
Comma Character on Expected Boundary
These devices provide 10-bit K28.5 character recognition and word alignment. The 10-bit word alignment is
enabled by forcing the SYNCEN terminal high. This enables the function that examines and compares serial
input data to the 7-bit synchronization pattern. The K28.5 character is defined by the 8b/10b coding scheme as a
pattern consisting of 0011 1110 10 (a negative number beginning with disparity), with the 7 MSBs (0011 111)
referred to as the comma character. The K28.5 character was implemented specifically for aligning data words.
As long as the K28.5 character falls within the expected 10-bit boundary, the received 10-bit data is properly
aligned and data realignment is not required. Figure 2 shows the timing characteristics of RBC0, RBC1, SYNC
and RD0–RD9 while synchronized. (Note: the K28.5 character is valid on the rising edge of RBC1).
Comma Character Not on Expected Boundary
If synchronization is enabled and a K28.5 character straddles the expected 10-bit word boundary, then word
realignment is necessary. Realignment or shifting the 10-bit word boundary truncates the character following the
misaligned K28.5, but the following K28.5 and all subsequent data is aligned properly as shown in Figure 4. The
RBC0 and RBC1 pulse widths are stretched or stalled in their current state during realignment. With this design,
the maximum stretch that occurs is 20 bit times. This occurs during a worst-case scenario when the K28.5 is
aligned to the falling edge of RBC1 instead of the rising edge. Figure 4 shows the timing characteristics of the
data realignment.
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