XRT7250 datasheet(143/463 Pages) EXAR

143 / 463 page

XRT7250

DS3/E3 FRAMER IC

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REV. 1.1.1

124

Bit 5 - REQB - (Receive Equalization Enable/Dis-

able Select)

This Read/Write bit-field allows the user to control the

state of the REQB output pin of the Framer device.

This output pin is intended to be connected to the

REQB input pin of the XRT7300 DS3/E3/STS-1 LIU

IC. If the user forces this signal to toggle "High”, then

the internal Receive Equalizer (within the XRT7300

device) will be disabled. Conversely, if the user forces

this signal to toggle "Low”, then the Receive Equalizer

(within the XRT7300 device) will be enabled.

The purpose of the internal Receive Equalizer (within

the XRT7300 device) is to compensate for the Fre-

quency-Dependent attenuation (e.g., cable loss), that

a line signal will experience as it travels through coax-

ial cable, from the transmitting to the receiving termi-

nal.

Writing a “1” to this bit-field causes the Framer device

to toggle the REQB output pin "High”. Writing a “0” to

this bit-field causes the Framer device to toggle the

REQB output pin "Low”.

For information on the criteria that should be used

when deciding whether to enable or disable the Re-

ceive Equalizer, please consult the XRT7300 DS3/

E3/STS-1 LIU IC Data Sheet.

NOTE: If the customer is not using the XRT7300 DS3/E3/

STS-1 IC, then this bit-field and the REQB output pin can

be used for other purposes.

Bit 4 - TAOS - (Transmit All Ones Signal)

This Read/Write bit-field allows the user to control the

state of the TAOS output pin of the Framer device.

This output pin is intended to be connected to the

TAOS input pin of the XRT7300 DS3/E3/STS-1 LIU

IC. if the user forces this signal to toggle "High”, then

the XRT7300 device will transmit an “All Ones” pat-

tern onto the line. Conversely, if the user commands

this output signal to toggle "Low” then the XRT7300

DS3/E3/STS-1 LIU IC will proceed to transmit data

based upon the data that it receives via the TxPOS

and TxNEG output pins (of the Framer IC).

Writing a “1” to this bit-field causes the TAOS output

pin to toggle "High”. Writing a “0” to this bit-field will

cause this output pin to toggle "Low”.

NOTE: If the customer is not using the XRT7300 DS3/E3/

STS-1 LIU IC, then this bit-field, and the TAOS output pin

can be used for other purposes.

Bit 3 - ENCODIS - (B3ZS/HDB3 Encoder Disable)

This Read/Write bit-field allows the user to control the

state of the ENCODIS output pin of the Framer de-

vice. This output pin is intended to be connected to

the ENCODIS input pin of the XRT7300 DS3/E3/

STS-1 LIU IC. If the user forces this signal to toggle

"High”, then the internal B3ZS/HDB3 encoder (within

the XRT7300 device) will be disabled. Conversely, if

the user commands this output signal to toggle "Low”,

then the internal B3ZS/HDB3 encoder (within the

XRT7300 device) will be enabled.

Writing a “1” to this bit-field causes the Framer IC to

toggle the Encodis output pin "High”. Writing a “0” to

this bit-field will cause the Framer IC to toggle this

output pin "Low”.

NOTES:

1. The B3ZS/HDB3 encoder, within the XRT7300

device is not to be confused with the B3ZS/HDB3

encoding capabilities that exists within the Transmit

DS3/E3 Framer block of the Framer IC.

2. The user is advised to disable the B3ZS/HDB3

encoder (within the XRT7300 IC) if the Transmit

and Receive DS3/E3 Framer (within the XRT7250)

are configured to operate in the B3ZS/HDB3 line

code.

3. If the customer is not using the XRT7300 DS3/E3/

STS-1 LIU IC, then this bit-field and the Encodis

output pin can be used for other purposes.

4. It is permissible to tie both the ENCODIS and

DECODIS input pins (of the XRT7300 device) to

the Encodis output pin of the XRT7250 DS3/E3

Framer IC.

Bit 2 - TxLEV (Transmit Line Build-Out Enable/

Disable Select)

This Read/Write bit-field allows the user to control the

state of the TxLEV output pin of the Framer device.

This output pin is intended to be connected to the Tx-

LEV input pin of the XRT7300 DS3/E3/STS-1 LIU IC.

Writing a “1” to this bit-field commands the Framer to

drive the TxLEV output pin "High”.

Writing a “0” to this bit-field commands the Framer to

drive this output signal "Low”.

If the user commands this signal to toggle "High”,

then the Transmit Line Build-Out circuitry, within the

XRT7300 device will be disabled. In this mode, the

XRT7300 LIU IC will generate unshaped (e.g.,

square) pulses out onto the line, via the TTIP and

TRING output pins.

Conversely, if the user commands this signal to toggle

"Low”, then the Transmit Line Build-Out circuitry, with-

in the XRT7300 device will be enabled. In this mode,

the XRT7300 device will generate shaped pulses on-

to the line, via the TTIP and TRING output pins.

In order to comply with the Isolated DSX-3 Pulse

Template requirements (per Bellcore GR-499-CORE),

the user is advised to set this bit-field to “0” if the ca-

ble length (between the transmit output of the

XRT7300 device and the DSX-3 Cross Connect Sys-

tem) is less than 225 feet. Conversely, the user is ad-

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