TLK2201, TLK2201I

ETHERNET TRANSCEIVERS

SLLS420C – JUNE 2000 – REVISED NOVEMBER 2001

6

POST OFFICE BOX 655303

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.