XRT7250 datasheet(29/463 Pages) EXAR

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XRT7250

DS3/E3 FRAMER IC

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REV. 1.1.1

TxLineClk

Transmit Line Interface Clock:

This clock signal is output to the Line Interface Framer, along with the TxPOS

and TxNEG signals. The purpose of this output clock signal is to provide the

LIU with timing information that it can use to generate the AMI pulses and

deliver them over the transmission medium to the Far-End Receiver. The user

can configure the source of this clock to be either the RxLineClk (from the

Receiver portion of the Framer) or the TxInClk input. The nominal frequency of

this clock signal is 34.368 MHz.

TxNEG

Transmit Negative Polarity Pulse:

The exact role of this output pin depends upon whether the Framer is operating

in the Unipolar or Bipolar Mode.

Unipolar Mode:

This output signal pulses "high" for one bit period, at the beginning of each

"outbound" DS3 or E3 frame. This output signal is at a logic "low" for all of the

remaining bit-periods of the "outbound" DS3 or E3 frames

Bipolar Mode:

This output pin functions as one of the two dual-rail output signals that com-

mands the sequence of pulses to be driven on the line. TxPOS is the other out-

put pin. This input is typically connected to the TNDATA input of the external

DS3/E3 Line Interface Unit IC. When this output is asserted, it will command

the LIU to generate a negative polarity pulse on the line.

TxPOS

Transmit Positive Polarity Pulse:

The exact role of this output pin depends upon whether the Framer is operating

in the Unipolar or Bipolar Mode.

Unipolar Mode:

This output pin functions as the "Single-Rail" output signal for the "outbound"

DS3 or E3 data stream. The signal, at this output pin, will be updated on the

"user-selected" edge of the TxLineClk signal.

Bipolar Mode:

This output pin functions as one of the two dual rail output signals that com-

mands the sequence of pulses to be driven on the line. TxNEG is the other out-

put pin. This input is typically connected to the TPDATA input of the external

DS3 or E3 Line Interface Unit IC. When this output is asserted, it will command

the LIU to generate a positive polarity pulse on the line

ENCODIS

Encoder (HDB3) Disable Output pin (intended to be connected to

the XRT7300 DS3/E3 Line Interface Unit IC).

This output pin is intended to be connected to the Encodis input pin of the

XRT7300 DS3/E3 Line Interface Unit IC. The user can control the state of this

output pin by writing a "0" or "1" to Bit 3 (Encodis) within the Line Interface

Driver Register (Address = 0x80). If the user commands this signal to toggle

"high" then it will disable the B3ZS/HDB3 encoder circuitry within the XRT7300

IC. Conversely, if the user commands this output signal to toggle "low", then the

B3ZS/HDB3 Encoder circuitry, within the XRT7300 IC will be enabled.

Writing a "1" to Bit 3 of the Line Interface Driver Register (Address = 0x80) will

cause this output pin to toggle "high". Writing a "0" to this bit-field will cause

this output pin to toggle "low".

The user is advised to disable the B3ZS/HDB3 encoder (within the XRT7300

IC) if the XRT7250 Framer IC has been configured to operate in the B3ZS/

HDB3 line code.

NOTE: If the customer is not using the XRT7300 DS3/E3 Line Interface Unit IC,

then he/she can use this output pin for a variety of other purposes.

PIN DESCRIPTION

PIN #NAME

TYPE

DESCRIPTION

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