XRT72L50 Datasheet, PDF (166/471 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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TABLE 17: DESCRIPTION OF METHOD 1 TRANSMIT OVERHEAD INPUT INTERFACE SIGNALS
NAME
TYPE
DESCRIPTION
TxOHIns
I Transmit Overhead Data Insert Enable input pin.
TxOH
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 samples the data at the TxOH input pin on the
falling edge of the TxOHClk 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 signal.
If the Terminal Equipment attempts to insert an overhead bit that cannot be accepted by the Trans-
mit 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 inser-
tion effort is ignored.
I Transmit Overhead Data Input pin:
The Transmit Overhead Data Input Interface accepts the overhead data via this input pin and in-
serts 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 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 sam-
ple the data at this input pin and this data is ignored.
TxOHClk O Transmit Overhead Input Interface Clock Output signal:
This output signal serves two purposes:
1. The Transmit Overhead Data Input Interface provides a rising clock edge on this signal one bit-
period prior to the instant that the Transmit Overhead Data Input Interface is processing an over-
head bit.
2. The Transmit Overhead Data Input Interface sample the data at the TxOH input on the falling
edge of this clock signal provided that the TxOHIns input pin is "High".
The Transmit Overhead Data Input Interface supplies a clock edge for all overhead bits within the
DS3 frame via the TxOHClk output signal. This includes those overhead bits that the Transmit
Overhead Data Input Interface will not accept from the Terminal Equipment.
TxOHFrame 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.
The purpose of this output signal is to alert the Terminal Equipment that the Transmit Overhead
Data Input Interface block is about to begin processing the overhead bits for a new DS3 frame.
Interfacing the Transmit Overhead Data Input Interface to the Terminal Equipment.
Figure 45 illustrates how one should interface the Transmit Overhead Data Input Interface to the Terminal
Equipment, when using Method 1.
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