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TLK2201AIRCPR Datasheet(PDF) 6 Page - Texas Instruments |
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TLK2201AIRCPR Datasheet(HTML) 6 Page - Texas Instruments |
6 / 21 page TLK2201A, TLK2201AI ETHERNET TRANSCEIVERS SLLS572 – JUNE 2003 6 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 receiver word alignment These devices use the IEEE 802.3 Gigabit Ethernet defined 10-bit K28.5 character (comma character) word alignment scheme. The following sections explain how this scheme works and how it realigns itself. 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 seven bit synchronization pattern. The K28.5 character is defined by the 8-bit/10-bit coding scheme as a pattern consisting of 0011111010 (a negative number beginning with disparity) with the 7 MSBs (0011111), 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 5. 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 5 shows the timing characteristics of the data realignment. DXX.X K28.5 DXX.X DXX.X K28.5 K28.5 DXX.X DXX.X DXX.X DXX.X DXX.X K28.5 DXX.X DXX.X K28.5 K28.5 DXX.X DXX.X 31 Bit Times Max Receive Path Latency Worst Case Misaligned K28.5 Misalignment Corrected INPUT DATA RBC0 RBC1 RD(0–9) SYNC Corrupt Data 30 Bit Times (Max) Figure 5. Word Realignment Timing Characteristics Waveforms Systems that do not require framed data may disable byte alignment by tying SYNCEN low. When a SYNC character is detected, the SYNC signal is brought high and is aligned with the K28.5 character. The duration of the SYNC pulse is equal to the duration of the data when in TBI mode. When in DDR mode the SYNC pulse is present for the entire RBC0 period. |
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