TNETE2201

1.25-GIGABIT ETHERNET TRANSCEIVER

SLLS267D – JUNE 1997 – REVISED FEBRUARY 1999

7

POST OFFICE BOX 655303

data reception (continued)

During a bus error condition or word alignment, the receive byte clocks RBC0 and RBC1 are stretched (never

truncated). When the incoming serial data does not meet its frequency requirements, then the receive byte clock

frequency is maintained at 62.5 MHz.

receive PLL operation

The receive PLL provides automatic locking to the incoming data. At power-up, the maximum initial lock time

is 500

µs. The PLL can also be initiated or set to phase lock to the externally supplied reference clock by enabling

lock-to-reference (LCKREFN). The lock-to-reference causes the receive PLL to lock to 10

× the reference clock

(REFCLK) input providing a PLL preset and reset capability.

If a transient occurs during normal operation (a transient being defined as any arbitrary phase shift in the

incoming data and/or a frequency wander of up to 200 ppm), the PLL recovers lock within 2.4

µs. Any condition

exceeding these values is considered a power-up scenario with the PLL recovering lock within 500

µs. With a

0.1

µF capacitor attached, the PLL recovers lock within 10 ms on power up.

receiver word alignment

The TNETE2201 uses a 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

The TNETE2201 provides 10-bit K28.5 character recognition and word alignment. The 10-bit word alignment

is enabled by forcing SYCNEN high. This enables the function that examines and compares ten bits of serial

input data to the K28.5 synchronization character. The K28.5 character is defined in the fibre channel standard

as a pattern consisting of 0011111010 (a negative number beginning 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 word boundary, the received 10-bit data is

properly aligned and data realignment is not required. Figure 1 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.

RBC0

RD0 – RD9

RBC1

SYNC

K28.5

Dxx.x

Dxx.x

Dxx.x

K28.5

Dxx.x

Figure 1. Synchronous Timing Characteristics Waveforms