XRT79L71IB datasheet(53/109 Pages) EXAR

53 / 109 page

XRT79L71

REV. 1.0.0

1-CHANNEL DS3/E3 ATM UNI/PPP/CLEAR-CHANNEL FRAMER IC - HARDWARE

PIN #

NAME

TYPE

DESCRIPTION

TRANSMIT LINE SIDE SIGNALS

R15

TxON

Transmit Driver ON - Channel n:

This input pin is used to either enable or disable the Transmit Output Driver within

the Transmit DS3/E3 LIU Block.

"Low" - Disables the Transmit Output Driver within the Transmit DS3/E3 LIU Block.

In this setting, the TTIP and TRING output pins will be tri-stated.

"High" - Enables the Transmit Output Driver within the Transmit DS3/E3 LIU Block.

In this setting, the TTIP and TRING output pins will be enabled.

NOTES:

Whenever the transmitters are turned off , the TTIP and TRING output

pins will be tri-stated.

These pins are internally pulled "High".

P16

DS3CLK

/SFMCLK

Clock Recovery PLL DS3 Reference Clock Input/12.288MHz SFM Reference

Clock Input:

The function of this input pin depends upon whether or not the XRT79L71 has

been configured to operate in the SFM (Single Frequency Mode) Mode, as

described below.

If the XRT79L71 is NOT operating in the Single-Frequency Mode

If the XRT79L71 has NOT been configured to operate in the SFM Mode, then this

input pin will functions as the Reference Clock for the Clock Recovery PLL and the

Jitter Attenuator PLL within the Receive DS3/E3 LIU Block, whenever the

XRT79L71 has been configured to operate in the DS3 Mode.

NOTE: For DS3/Non-SFM Modes of operation, the user is expected to supply a

44.736MHz ± 20ppm clock signal to this input pin.

If the XRT79L71 is operating in the Single-Frequency Mode

If the user has configured the XRT79L71 to operate in the SFM Mode, then the

user MUST apply a clock signal with a frequency of 12.288MHz ± 20ppm to this

input pin. The SFM Synthesizer block (within the Receive DS3/E3 LIU Block) will

then synthesize one of the appropriate line rate frequencies (e.g., 34.368MHz for

E3 and 44.736MHz for DS3) based upon this 12.288MHz Reference Clock

source.

NOTE: If the user does not intend to operate the XRT79L71 in the SFM Mode, nor

the DS3 Mode, tie this input pin to GND.

XRT79L71IB Datasheet(PDF) 53 Page - Exar Corporation

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