XRT72L56 Datasheet, PDF (296/486 Pages) Exar Corporation – SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

XRT72L56
SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
REV. P1.1.2
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PRELIMINARY
available. When using Method 2, either the TxInClk
or RxOutClk signal is used to sample the overhead
bits and signals which are input to the Transmit Over-
head Data Input Interface. Method 2 involves the use
of the following signals:
• TxOH
• TxInClk
• TxOHFrame
• TxOHEnable
Each of these signals are listed and described in
Table 51.
TABLE 51: DESCRIPTION OF METHOD 2 TRANSMIT OVERHEAD INPUT INTERFACE SIGNALS
NAME
TxOHEn-
able
TxO-
HFrame
TxOHIns
TxOH
TYPE
Output
Output
Input
Input
DESCRIPTION
Transmit Overhead Data Enable Output pin
The XRT72L56 will assert this signal, for one TxInClk period, just prior to the instant that the
Transmit Overhead Data Input Interface is processing an overhead bit.
Transmit Overhead Input Interface Frame Boundary Indicator Output:
This output signal pulses "High" when the XRT72L56 is processing the last bit within a given DS3
frame.
Transmit Overhead Data Insert Enable input pin.
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 TxInClk 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 TxOHIns
signal, at a time when one of these non-insertable overhead bits are being processed), that par-
ticular 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.
Interfacing the Transmit Overhead Data Input Interface
to the Terminal Equipment
Figure 115 illustrates how one should interface the
Transmit Overhead Data Input Interface to the Termi-
nal Equipment when using Method 2.
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