TNETE2201B

1.25GIGABIT ETHERNET TRANSCEIVER

SLLS367D − JUNE 1999 − REVISED AUGUST 2007

8

POST OFFICE BOX 655303

comma character not on expected boundary

When 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 2. The 10b specification requires that RCLK cycles can not be truncated and can only be stretched

or stalled in their current state during realignment. With this design the maximum stretch that occurs is an extra

10 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. This system transmits a minimum of three consecutively ordered K28.5 data sets

between frames and ensures that the receiver sees at least two of K28.5 sets (the fabric is allowed to drop one).

Figure 2 shows the timing characteristics of the data realignment.

Systems that do not require framed data can disable byte alignment by tying SYNCEN low.

When a synchronization character is detected the SYNC signal is asserted high and is aligned with the K28.5

character. The duration of the SYNC-signal pulse is equal to the duration of the data which is half an RCLK

period.

RBC0

RBC1

SYNC

Serial Rx Data Stream

DIN_RxP − DIN_RxN

K28.5

Dxx.x

Dxx.x

Dxx.x

K28.5

Dxx.x

RD0 − RD9

K28.5

Dxx.x

Dxx.x

Dxx.x

Dxx.x

K28.5

20 Bit Times

(MAX)

Typical Receive

Path Latency = 18 ns

Dxx.x

Dxx.x

Dxx.x

Worst Case

Misaligned K28.5

Corrupted Data

Misalignment

Corrected

10 Bit Times

10 Bit Times

Dxx.x

K28.5

K28.5

Dxx.x

K28.5

Figure 2. Word Realignment Timing Characteristics Waveforms

data reception latency

The serial-to-parallel data latency is the time from when the first bit arrives at the receiver until it is output in the

aligned parallel word with RD0 received as first bit. The receive latency is typically 18 ns.