XRT7250 datasheet(296/463 Pages) EXAR

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XRT7250

DS3/E3 FRAMER IC

REV. 1.1.1

277

The Transmit E3 LIU Interface block can transmit data

to the LIU IC or other external circuitry via two differ-

ent output modes: Unipolar or Bipolar. If the user se-

lects Unipolar (or Single Rail) mode, then the con-

tents of the E3 Frame is output, in a binary (NRZ

manner) data stream via the TxPOS pin to the LIU IC.

The TxNEG pin will only be used to denote the frame

boundaries. TxNEG will pulse "High" for one bit peri-

od, at the start of each new E3 frame, and will remain

"Low" for the remainder of the frame. Figure 122 pre-

sents an illustration of the TxPOS and TxNEG signals

during data transmission while the Transmit E3 LIU

Interface block is operating in the Unipolar mode.

This mode is sometimes referred to as Single Rail

mode because the data pulses only exist in one po-

larity: positive.

When the Transmit E3 LIU Interface block is operating

in the Bipolar (or Dual Rail) mode, then the contents

of the E3 Frame is output via both the TxPOS and Tx-

NEG pins. If the Bipolar mode is chosen, then E3 da-

ta can be transmitted to the LIU via one of two differ-

ent line codes: Alternate Mark Inversion (AMI) or High

Density Bipolar -3 (HDB3). Each one of these line

codes will be discussed below. Bipolar mode is

sometimes referred to as Dual Rail because the data

pulses occur in two polarities: positive and negative.

FIGURE 121. A SIMPLE ILLUSTRATION OF THE TRANSMIT E3 LIU INTERFACE BLOCK

From Transmit E3

Framer Block

TxPOS

TxNEG

TxLineClk

Transmit E3

LIU Interface

Block

FIGURE 122. THE BEHAVIOR OF TXPOS AND TXNEG SIGNALS DURING DATA TRANSMISSION WHILE THE TRANSMIT

DS3 LIU INTERFACE IS OPERATING IN THE UNIPOLAR MODE

TxPOS

TxNEG

TxLineClk

Data

Frame Boundary

XRT7250 Datasheet(PDF) 296 Page - Exar Corporation

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