XRT79L72 Datasheet, PDF (42/72 Pages) Exar Corporation – 2 - CHANNEL DS3/E3 ATM UNI/PPP COMBO IC

XRT79L72
REV. P1.0.2
PRELIMINARY
xr
2 - CHANNEL DS3/E3 ATM UNI/PPP COMBO IC
PIN #
NAME
TYPE
DESCRIPTION
TRANSMIT LINE SIDE SIGNALS
AE4
TxON
I Transmit Driver ON - Channel n:
This input pin is used to either enable or disable the Transmit Output Drivers of the
XRT79L72.
"Low" - Disables the XRT79L72 Transmit Output Drivers. In this setting, the TTIP
and TRING output pins will be tri-stated.
"High" - Enables the XRT79L72 Transmit Output Drivers if the individual register
bits are set to "1". In this setting, the TTIP and TRING output pins will be enabled.
NOTES:
1. Whenever the transmitters are turned off , the TTIP and TRING output
pins will be tri-stated.
2. These pins are internally pulled high.
Y5
DS3CLK/
I ^{Clock Recovery PLL DS3 Reference Clock Input/12.288MHz SFM Ref-}
SFMCLK
erence 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 Fre-
quency Mode) Mode, as described below.
If the XRT79L72 device is NOT operating in the Single-Frequency ModeIf
the XRT79L72 has NOT been configured to operate in the SFM Mode,
then this input pin will functions as the Reference Clock for the Clock Re-
covery PLL and the Jitter Attenuator PLL within the Receive DS3/E3 LIU
Block, whenever the XRT79L72 device 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 XRT79L72 device is operat-
ing in the Single-Frequency Mode
If 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
12.288MHz ± 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 XRT79L72 device in the SFM
Mode, nor the DS3 Mode, then he/she should tie this input pin to GND.
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