XRT7250 Datasheet, PDF (27/463 Pages) Exar Corporation – DS3/E3 FRAMER IC

XRT7250 DS3/E3 FRAMER IC
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REV. 1.1.1
PIN DESCRIPTION
PIN #
52
NAME
TxOHClk
53
TxOHIns
54
TxOH
55
TxOHInd
TYPE
DESCRIPTION
O Transmit Overhead Clock
This output signal serves two purposes:
1. The Transmit Overhead Data Input Interface block will provide a rising clock
edge on this signal, one bit-period prior to the start to the instant that the
“Transmit Overhead Data Input Interface” block is processing an overhead bit.
2. The Transmit Overhead Data Input Interface will sample the data at the
“TxOH” input pin, on the falling edge of this clock signal (provided that the
“TxOHIns” input pin is “HIGH”).
NOTE: The Transmit Overhead Data Input Interface block will supply a clock
edge for all overhead bits within the DS3 or E3 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.
I Transmit Overhead Data Insert Input.
Asserting this input signal (e.g., setting it "high") enables the Transmit Over-
head Data Input Interface to accept "overhead" data from the Terminal Equip-
ment. 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 "TxOHClk" 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 Termi-
nal 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.
I Transmit Overhead 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 "out-
bound" DS3 or 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
O Transmit Overhead Data Indicator.
This output pin will pulse "high" one-bit period prior to the time that the Transmit
Section of the XRT7250 will be processing an Overhead bit. The purpose of
this output pin is to warn the Terminal Equipment that, during the very next bit-
period, the XRT7250 is going to be processing an "Overhead" bit and will be
ignoring any data that is applied to the "TxSer" input pin.
NOTE: For DS3 applications, this output pin is only active if the XRT7250 is
operating in the "Serial" Mode. This output pin will be pulled "low" if the device
is operating in the "Nibble-Parallel" Mode.
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