XRT72L71 datasheet(21/102 Pages) EXAR

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XRT72L71

DS3 ATM UNI/CLEAR CHANNEL FRAMER

REV. 1.1.0

108

TxOHInd/

TxPFrame

Transmit Overhead Data Indicator/Transmit PLCP Frame Boundary Indi-

cator—Output:

The exact functionality of this output pin depends upon whether the

XRT72L71 Framer IC is operating in the Clear Channel or ATM Uni Mode.

Clear Channel Mode:

In the Clear Channel Mode, this pin serves as the transmit OH Indication for

the external interface. This pin is pulsed for one bit period of DS3 clock to indi-

cate to the external device that the transmit input interface is going to process

OH data at the rising edge of next clock. When the external interface samples

TxOHInd as “High” With the rising edge of DS3 Clk; it is expected NOT to pro-

vide useful payload data bit on TxSer pin. Instead it can provide correspond-

ing OH data bit on TxSer input. However, in that case the user has to program

a register bit to configure XRT72L71 to accept the OH data from the TxSer

input. Otherwise, the OH data will be geaerated internally or be taken from

the TxOH pin if TxOHIns is “High”. This pin is pulsed "High" for one bit period

prior to all DS3 OH bit positions.

ATM UNI Mode:

In ATM UNI mode of operation, this pin functions as Transmit PLCP Frame

signal which pulses "High" once for each outbound PLCP frame, when the last

nibble is being routed.

109

TxPOS

Transmit Positive Polarity Pulse: The exact role of this output pin depends

upon whether the UNI is operating in the Unipolar or Bipolar Mode.

Unipolar Mode: This output pin functions as the “Single-Rail” output signal for

the “outbound” DS3 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 sig-

nals that commands the sequence of pulses to be driven on the line. TxNEG

is the other output pin. This input is typically connected to the TPDATA input of

the external DS3 Line Interface Unit IC. When this output is asserted, it will

command the LIU to generate a positive polarity pulse on the line.

110

TxPOHFrame

Transmit PLCP Frame Path Overhead Byte Serial Input Port—Beginning

of Frame indicator. This output pin, along with the TxPOH, TxPOHClk, and

TxPOHIns pins comprise the “Transmit PLCP Frame POH Byte Insertion”

serial input port. This particular pin will pulse “High” when the “Transmit PLCP

POH Byte Insertion” serial input port is expecting the first bit of the Z6 byte at

the TxPOH input pin.

NOTE: This output pin is only active if the XRT72L71 has been configured to

operate in the “ATM UNI” Mode.

111

TxNEG

Transmit Negative Polarity Pulse: The exact role of this output pin depends

upon whether the UNI is operating in the Unipolar or Bipolar Mode.

Unipolar Mode: This output signal pulses “High” for one bit period, at the end

of each “outbound” DS3 frame. This output signal is at a logic “Low” for all of

the remaining bit-periods of the “outbound” DS3 frames.

Bipolar Mode: This output pin functions as one of the two dual-rail output sig-

nals that commands the sequence of pulses to be driven on the line. TxPOS is

the other output pin. This input is typically connected to the TNDATA input of

the external DS3 Line Interface Unit IC. When this output is asserted, it will

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

PIN DESCRIPTION (CONTINUED)

PIN NO.

SYMBOL

TYPE

DESCRIPTION

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