XRT79L72 Datasheet, PDF (43/72 Pages) Exar Corporation – 2 - CHANNEL DS3/E3 ATM UNI/PPP COMBO IC

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PRELIMINARY
2 - CHANNEL DS3/E3 ATM UNI/PPP COMBO IC
XRT79L72
REV. P1.0.2
PIN #
Y1
AD10
AD14
AE10
AE14
NAME
E3CLK
TTIP_0
TTIP_1
TRING_0
TRING_1
TYPE
DESCRIPTION
I Clock Recovery PLL E3 Reference Clock Input:
The exact function of this input pin depends upon whether or not the XRT79L72
device has been configured to operate in the SFM (Single-Frequency Mode)
Mode, as described below.If the XRT79L72 device is NOT operating in the Single-
Frequency ModeIf the XRT79L72 device has NOT been configured to operate in
the SFM Mode, then this input pin will function as a Reference Clock signal for the
Clock Recovery PLL and the Jitter Attenuator PLL within the Receive DS3/E33
LIU Block, whenever the XRT79L72 device has been configured to operate in the
E3 Mode.
NOTE: For E3/Non-SFM Modes of operation, the user is expected to supply a
34.368MHz ± 20ppm clock signal to this input pin.
If the XRT79L72 device is operating in the Single-Frequency ModeIf the user has
configured the XRT79L72 device to operate in the SFM Mode, then the user
MUST apply a clock signal with a frequency of 12.288 ± 20ppm to the "DS3CLK/
SFMCLK" input pin (Ball Y5). Additionally, the user MUST tie this input pin to
GND.
NOTE: If the user only intends to operate the XRT79L72 device in the DS3/Non-
SFM Mode, then the user should tie this input pin to GND.
O Transmit Output - Positive Polarity Signal:
O These output pins, along with the TRING output pins, function as the Transmit
DS3/E3 output signal drivers for the XRT79L72.
The user is expected to connect these signals and the TRING output signals to a
1:1 transformer.
Whenever the Transmit Section of the XRT79L72 generates and transmits a posi-
tive-polarity pulse onto the line, these output pins will be pulsed to a "higher-volt-
age" than the TRING output pins.
Conversely, whenever the Transmit Section of the XRT79L72 generates and
transmit a negative-polarity pulse onto the line, these output pins will be pulsed to
a "lower-voltage" than the TRING output pins.
NOTE: These output pins will be tri-stated whenever the user sets the TxONn
input pin (or bit-field) to "0".
O Transmit Output - Negative Polarity Signal:
O These output pins along with the TTIP output pins, function as the Transmit DS3/
E3 output signal drivers for the XRT79L72.
The user is expected to connect these signals and the TTIP output signals to a 1:1
transformer.
Whenever the Transmit Section of the XRT79L72 generates and transmits a pos-
itive-polarity pulse onto the line, these output pins will be pulsed to a "lower-volt-
age" than the TTIP output pins.
Conversely, whenever the Transmit Section of the XRT79L72 generates and
transmit a negative-polarity pulse onto the line, these output pins will be pulsed to
a "higher-voltage" than the TTIP output pins.
NOTE: These output pins will be tri-stated whenever the user sets the TxONn
input pin (or bit-field) to "0".
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