XRT72L50 Datasheet, PDF (278/471 Pages) Exar Corporation – SINGLE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
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5.2.2.2 Method 2 - Using the TxInClk and TxOHEnable Signals
Method 1 requires the use of an additional clock signal, TxOHClk. However, there may be a situation in which
the user does not wish to add this extra clock signal to their design, in order to use the Transmit Overhead Data
Input Interface. Hence, Method 2 is 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 Overhead 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 47.
TABLE 47: DESCRIPTION OF METHOD 2 TRANSMIT OVERHEAD INPUT INTERFACE SIGNALS
NAME
TxOHEnable
TxOHFrame
TxOHIns
TxOH
TYPE
DESCRIPTION
Output Transmit Overhead Data Enable Output pin
The XRT72L50 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.
Output Transmit Overhead Input Interface Frame Boundary Indicator Output:
This output signal pulses "High" when the XRT72L50 is processing the last bit within a given
E3 frame.
Input
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 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 TxO-
HClk 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 particular insertion effort will be ignored.
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 E3 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 103 illustrates how one should interface the Transmit Overhead Data Input Interface to the Terminal
Equipment when using Method 2.
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