XRT72L50 Datasheet, PDF (171/471 Pages) Exar Corporation – SINGLE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
4.2.2.2 Method 2 - Using the TxInClk and TxOHEnable Signals
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 Overhead Data Input Interface. Method 2 involves the use of the following
signals:
• TxOH
• TxInClk
• TxOHFrame
• TxOHEnable
• TxOHIns
These signals are described in Table 19.
TABLE 19: DESCRIPTION OF METHOD 2 TRANSMIT OVERHEAD INPUT INTERFACE SIGNALS
NAME
TxOHEnable
TxInClk
TxOHFrame
TxOHIns
TxOH
TYPE
DESCRIPTION
O Transmit Overhead Data Enable Output pin
The XRT72L50 asserts this signal for one TxInClk period just prior to the instant that the
Transmit Overhead Data Input Interface is processing an overhead bit.
I
Transmit Section Timing Reference Clock Input pin:
The Transmit Section of the XRT72L50 can be configured to use this clock signal as the Tim-
ing Reference. If this configuration is selected, then the XRT72L50 uses this clock signal to
sample the data on the TxSer input pin and a DS3 or E3 clock signal must be applied to this
pin.
O Transmit Overhead Input Interface Frame Boundary Indicator Output:
This output signal pulses "High" when the XRT72L50 is processing the last bit within a given
DS3 frame.
I
Transmit Overhead Data Insert Enable input pin.
Asserting this input signal (e.g., setting it "High") enables the Transmit Overhead Data Input
Interface to accept overhead data from the Terminal Equipment. In other words, while this
input pin is "High", the Transmit Overhead Data Input Interface samples the data at the
TxOH input pin on the falling edge of the TxInClk output signal.
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 sig-
nal.
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 is ignored.
I
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 samples the data
at this input pin (TxOH) on the falling edge of the TxOHClk output pin.
If the TxOHIns pin is pulled "Low", then the Transmit Overhead Data Input Interface will NOT
sample the data at this input pin (TxOH) and this data is ignored.
Interfacing the Transmit Overhead Data Input Interface to the Terminal Equipment
Figure 47 illustrates how one should interface the Transmit Overhead Data Input Interface to the Terminal
Equipment when using Method 2.
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