XRT72L13 Datasheet, PDF (270/370 Pages) Exar Corporation – M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC

XRT72L13
M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC
REV. P1.0.6
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PRELIMINARY
Upon detection of the very next rising edge of the "Tx-
OHClk" clock signal (designated as "clock edge 1" in
Figure 77 ), the Terminal Equipment will negate the
"TxOHIns" signal (e.g., toggles it "low") and will cease
inserting data into the "Transmit Overhead Data Input
Interface", until "rising clock edge # 8" (of the "TxO-
HClk" signal). According to Table 15 , "rising clock
edge # 8" indicates that the XRT72L13 is just about
ready to process the second "X" bit within the "out-
bound" DS3 frame. Once again, in order to facilitate
the transmission of the "Yellow Alarm" this "X-Bit"
must also be set to "0". Hence, the Terminal Equip-
ment will (once again) implement the following steps,
concurrently.
a. Assert the "TxOHIns" input pin by setting it "high".
b. Set the "TxOH" input to "0".
Once again, after the Terminal Equipment has ap-
plied these signals these signals; the XRT72L13 will
sample the data on both the "TxOHIns" and "TxOH"
signal upon the very next falling edge of "TxOHClk"
(designated as "8-" in Figure 77 ). Once the
XRT72L13 has sampled this data, it will then insert a
"0" into the second "X" bit position, in the "outbound"
DS3 frame.
4.2.2.2 Method 2 - Using the TxInClk and TxO-
HEnable Signals
Method 1 requires the use of an additional clock sig-
nal, "TxOHClk". However, there may be a situation in
which the user does not wish to accommodate and
process 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 16 .
TABLE 16: DESCRIPTION OF "METHOD 2" TRANSMIT OVERHEAD INPUT INTERFACE SIGNALS
NAME
TYPE
DESCRIPTION
TxOHEnable Output Transmit Overhead Data Enable Output pin
The XRT72L13 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 XRT72L13 is processing the last bit within a
given DS3 frame.
TxOHIns Input Transmit Overhead Data Insert Enable input pin.
TxOH
Input
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 "TxO-
HIns" signal, at a time when one of these "non-insertable" overhead bits are being processed);
that particular 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.
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