XRT7250 Datasheet, PDF (194/463 Pages) Exar Corporation – DS3/E3 FRAMER IC

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DS3/E3 FRAMER IC
FIGURE 66. A SIMPLE ILLUSTRATION OF THE TRANSMIT DS3 LIU INTERFACE BLOCK
XRT7250
REV. 1.1.1
From Transmit DS3
Framer Block
Transmit DS3
LIU Interface
Block
TxPOS
TxNEG
TxLineClk
The Transmit DS3 LIU Interface block can transmit
data to the LIU IC or other external circuitry via two
different output modes: Unipolar or Bipolar. If the Un-
ipolar (or Single Rail) mode is selected, then the con-
tents of the DS3 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 DS3 frame, and will re-
main "Low" for the remainder of the frame. Figure 67
presents an illustration of the TxPOS and TxNEG sig-
nals during data transmission while the Transmit DS3
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.
FIGURE 67. THE BEHAVIOR OF TXPOS AND TXNEG SIGNALS DURING DATA TRANSMISSION WHILE THE TRANSMIT
DS3 LIU INTERFACE IS OPERATING IN THE UNIPOLAR MODE
Data _{1 0 1 1 0 0 1 0 0 1 1 1 0 1 0 1 0 0 1}
TxPOS
1 10
01
TxNEG
TxLineClk
Frame Boundary
When the Transmit DS3 LIU Interface block is operat-
ing in the Bipolar (or Dual Rail) mode, then the con-
tents of the DS3 Frame is output via both the TxPOS
and TxNEG pins. If the Bipolar mode is chosen, then
the DS3 data to the LIU can be transmitted via one of
two different line codes: Alternate Mark Inversion
(AMI) or Binary - 3 Zero Substitution (B3ZS). Each
one of these line codes will be discussed below. Bi-
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