XRT79L72 Datasheet, PDF (13/72 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 #
G2
D23
R2
M24
NAME
TxOHFrame_0/
TxHDLCClk_0
TxOHFrame_1/
TxHDLCClk_1
TxOHEnable_0/
TxHDLCDat0_7
TxOHEnable_1/
TxHDLCDat0_2
TYPE
DESCRIPTION
O Transmit Overhead Framing Pulse/Transmit HDLC Controller Clock Output
pin:
O ^{The function of these output pins depend upon whether or not the XRT79L72}
has been configured to operate in the High-Speed HDLC Controller Mode.
Non-High-Speed HDLC Controller Mode - TxOHFrame:
These output pins pulse high for one TxOHClk period coincident with the instant
the Transmit Overhead Data Input Interface would be accepting the first over-
head bit within an outbound DS3 or E3 frame.
High Speed HDLC Controller Mode - TxHDLCClk:
This output pin functions as the "demand" clock output signal for the "Transmit
HDLC Controller" byte-wide input interface. This clock signal is ultimately
derived from either the TxInClk clock signal (for Local-Timing Applications) or the
RxOutClk clock signal (for Loop-Timing Applications). Hence, the frequency of
this clock signal is nominally one-eight of that of the TxInClk or the RxOutClk sig-
nals.
The Transmit HDLC Controller block will sample the contents of the Transmit
HDLC Controller byte-wide input interface, upon the rising edge of these clock
output signals. Therefore, the local terminal equipment should be designed to
output data onto the TxHDLCDatn_[7:0] bus upon the falling edge of these clock
output signals.
I/O Transmit Overhead Enable Output indicator/Transmit HDLC Controller Data
Bit 7 Input:
I/O ^{The function of these input pins depend upon whether or not the XRT79L72 is}
configured to operate in the High Speed HDLC Controller Mode.
Non-High Speed HDLC Controller Mode - TxOHEnable:
The XRT79L72 will assert these output pins, for one TxInClk period, just prior to
the instant that the Transmit Overhead Data Input Interface will be sampling and
processing an overhead bit.
If the local terminal equipment intends to insert its own value for an overhead bit,
into the outbound DS3 or E3 data stream, then it is expected to sample the state
of these signals, upon the falling edge of TxInClk. Upon sampling the TxOHEn-
able signal "High", the local terminal equipment should;
(1) place the desired value of the overhead bit onto the TxOH input pin and
(2) assert the TxOHIns input pin.
The Transmit Overhead Data Input Interface block will sample and latch the data
on the TxOH signal, upon the rising edge of the very next TxInClk input signal.
High-Speed HDLC Controller Mode - TxHDLCDat_7:
If the XRT79L72 is configured to operate in the High-Speed HDLC Controller
mode, then the local terminal equipment will be provided with a byte-wide Trans-
mit HDLC Controller byte-wide input interface. These input pins will function as
Bit 7 (the MSB) within this byte wide interface.
Data, residing on the Transmit HDLC Controller byte wide input interface, will be
sampled upon the rising edge of the TxHDLCClk output signals.
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