XRT74L73 Datasheet, PDF (311/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

PRELIMINARY
XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
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 66 .
TABLE 66: 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 XRT74L73 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 XRT74L73 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
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 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 122 illustrates how one should interface the
Transmit Overhead Data Input Interface to the Termi-
nal Equipment when using Method 2.
312