XRT79L74 Datasheet, PDF (23/70 Pages) Exar Corporation – 4 - CHANNEL DS3/E3 ATM UNI/PPP COMBO IC

PRELIMINARY
4 - CHANNEL DS3/E3 ATM UNI/PPP COMBO IC
XRT79L74
REV. P1.0.0
PIN #
B10
NAME
TxUClk/
TxPClk
TYPE
DESCRIPTION
I Transmit UTOPIA Interface Clock/Transmit POS-PHY Interface Clock Input:
The function of this input pin depends upon whether the XRT79L74 has been
configured to operate in the ATM UNI or in the PPP Mode.
ATM UNI Mode - TxUClk:
The Transmit UTOPIA Interface clock is used to latch the data on the Transmit
UTOPIA Data bus, into the Transmit UTOPIA Interface block. This clock signal is
also used as the timing source for circuitry used to process the ATM cell data into
and through the TxFIFO.
During Multi-PHY operation, the data on the Transmit UTOPIA Address bus pins
is sampled on the rising edge of TxUClk.
PPP Mode - TxPClk:
The Transmit POS-PHY Interface clock is used to latch the data on the Transmit
POS-PHY Data bus, into the Transmit POS-PHY Interface block. This clock sig-
nal is also used as the timing source for circuitry used to process the Packet data
into and through the TxFIFO.
NOTE: The XRT79L74 device can support TxUClk or TxPClk clock frequencies
of up to 50MHz.
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