XRT7250 datasheet(397/463 Pages) EXAR

397 / 463 page

XRT7250

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DS3/E3 FRAMER IC

REV. 1.1.1

378

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 180 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 the E3

data can be transmitted to the LIU via one of two dif-

ferent 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

FIGURE 179. A SIMPLE ILLUSTRATION OF THE TRANSMIT E3 LIU INTERFACE BLOCK

From Transmit E3

Framer Block

TxPOS

TxNEG

TxLineClk

Transmit E3

LIU Interface

Block

FIGURE 180. 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

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