XRT72L56 Datasheet, PDF (398/486 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
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 75.
TABLE 75: DESCRIPTION OF METHOD 1 TRANSMIT OVERHEAD INPUT INTERFACE SIGNALS
NAME
TYPE
DESCRIPTION
TxOHEnable Output ^{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.
TxOHFrame
Output
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.
TxOHIns
Input
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.
TxOH
Input
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 sam-
ple 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 172 illustrates how one should interface the
Transmit Overhead Data Input Interface to the Termi-
nal Equipment when using Method 2.
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