XRT72L13 Datasheet, PDF (265/370 Pages) Exar Corporation – M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC

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PRELIMINARY
XRT72L13
M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC
REV. P1.0.6
TABLE 14: DESCRIPTION OF "METHOD 1" TRANSMIT OVERHEAD INPUT INTERFACE SIGNALS
NAME
TYPE
DESCRIPTION
TxOHIns Input Transmit Overhead Data Insert Enable input pin.
TxOH
Input
Asserting this input signal (e.g., setting it "high") enables the Transmit Overhead Data Input Inter-
face to accept "overhead" data from the Terminal Equipment. In other words, while this input pin
is "high", the Transmit Overhead Data Input Interface will sample the data at the "TxOH" input pin,
on the falling edge of the "TxOHClk" output signal.
Conversely, setting this pin "low" configures the "Transmit Overhead Data Input Interface" to NOT
sample (e.g., ignore) the data at the "TxOH" input pin, on the falling edge of the "TxOHClk" output
signal.
NOTE: If the Terminal Equipment attempts to insert an overhead bit that cannot be accepted by
the "Transmit Overhead Data Input Interface" (e.g., if the Terminal Equipment asserts the "TxO-
HIns" signal, at a time when one of these "non-insertable" overhead bits are being processed);
that particular insertion effort will be ignored.
Transmit Overhead Data Input pin:
The Transmit Overhead Data Input Interface accepts the overhead data via this input
pin, and inserts into the "overhead" bit position within the very next "outbound" DS3
frame. If the "TxOHIns" pin is pulled "high", the Transmit Overhead Data Input Interface
will sample the data at this input pin (TxOH), on the falling edge of the "TxOHClk" output
pin. Conversely, if the "TxOHIns" pin is pulled "low", then the Transmit Overhead Data
Input Interface will NOT sample the data at this input pin (TxOH). Consequently, this
data will be ignored.
TxOHClk Output Transmit Overhead Input Interface Clock Output signal:
TxOHFrame
Output
This output signal serves two purposes:
1. The Transmit Overhead Data Input Interface will provide a rising clock edge on this signal, one
bit-period prior to the instant that the "Transmit Overhead Data Input Interface" is processing an
overhead bit.
2. The Transmit Overhead Data Input Interface will sample the data at the TxOH input, on the fall-
ing edge of this clock signal (provided that the TxOHIns input pin is "high").
NOTE: The Transmit Overhead Data Input Interface will supply a clock edge for all overhead bits
within the DS3 frame (via the “TxOHClk” output signal). This includes those overhead bits that
the "Transmit Overhead Data Input Interface" will not accept from the Terminal Equipment.
Transmit Overhead Input Interface Frame Boundary Indicator Output:
This output signal pulses "high" when the XRT72L13 is processing the last bit within a
given DS3 frame.
The purpose of this output signal is to alert the Terminal Equipment that the Transmit
Overhead Data Input Interface” block is about to begin processing the overhead bits for
a new DS3 frame.
Interfacing the "Transmit Overhead Data Input In-
terface" to the Terminal Equipment.
Figure 76 illustrates how one should interface the
"Transmit Overhead Data Input Interface" to the Ter-
minal Equipment, when using "Method 1".
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