XRT7250 Datasheet, PDF (175/463 Pages) Exar Corporation – DS3/E3 FRAMER IC

XRT7250 DS3/E3 FRAMER IC
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REV. 1.1.1
b. Set the TxOH input to 0.
Once again, after the Terminal Equipment has ap-
plied these signals, the XRT7250 will sample the data
on both the TxOHIns and TxOH signal upon the very
next falling edge of TxOHClk (designated as 8- in
Figure 58). Once the XRT7250 has sampled this da-
ta, it will then insert a "0" into the second X bit posi-
tion, 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 sam-
ple 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 22.
TABLE 22: DESCRIPTION OF METHOD 2 TRANSMIT OVERHEAD INPUT INTERFACE SIGNALS
NAME
TYPE
DESCRIPTION
TxOHEnable Output Transmit Overhead Data Enable Output pin
The XRT7250 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 XRT7250 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 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 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 59 illustrates how one should interface the
Transmit Overhead Data Input Interface to the Termi-
nal Equipment when using Method 2.
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