XRT74L74 Datasheet, PDF (199/498 Pages) Exar Corporation – 4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
ADVANCED CONFIDENTIAL
XRT74L74
REV. P1.1.1
TABLE 34: LISTING AND DESCRIPTION OF THE PINS ASSOCIATED WITH THE TRANSMIT PAYLOAD DATA INPUT
INTERFACE
SIGNAL NAME
TxFrameRef
RxOutClk
TYPE
DESCRIPTION
Input
Transmit Frame Reference Input:
The XRT74L74 permits the configuration of the Transmit Section to use this input pin as a
frame reference. If this configuration is selected, then the Transmit Section will initiate its
transmission of a new DS3 frame, upon the rising edge of this signal.
The purpose of this input pin is to permit the Terminal Equipment to maintain Transmit DS3
Framing alignment control over the XRT74L74.
Output _{Loop-Timed Timing Reference Clock Output pin:}
The Transmit Section of the XRT74L74 can be configured to use the RxLineClk signal as the
Timing Reference (e.g., loop-timing). If this configuration is selected, then the XRT74L74 will:
• Output a 44.736 MHz clock signal via this pin, to the Terminal Equipment.
• Sample the data on the TxSer input pin, upon the rising edge of this clock signal.
Operation of the Transmit Payload Data Input In-
terface
The Transmit Payload Data Input Interface is ex-
tremely flexible, in that it permits the following config-
uration options.
• The Serial or the Nibble-Parallel Interface Mode
• The Loop-Timing or the TxInClk (Local Timing)
Mode
Further, if the XRT74L74 has been configured to op-
erate in the TxInClk (Local Timing) mode, then there
are two additional options.
• The XRT74L74 functions as the Frame Master
(e.g., it dictates when the Terminal Equipment will
initiate the transmission of data within a new DS3
frame).
• The XRT74L74 functions as the Frame Slave (e.g.,
the Terminal Equipment will dictate when the
XRT74L74 initiates the transmission of a new DS3
frame).
Given these three set of options, the Transmit Termi-
nal Input Interface can be configured to operate in
one of the six (6) following modes.
• Mode 1 - Serial/Loop-Timed Mode
• Mode 2 - Serial/Local-Timed/Frame Slave Mode
• Mode 3 - Serial/Local-Timed/Frame Master Mode
• Mode 4 - Nibble/Loop-Timed Mode
• Mode 5 - Nibble/Local-Timed/Frame Slave Mode
• Mode 6 - Nibble/Local-Timed/Frame Master Mode
Each of these modes are described, in detail, below.
5.2.1.1 Mode 1 - The Serial/Loop-Timing Mode
The Behavior of the XRT74L74
If the XRT74L74 has been configured to operate in
this mode, then the XRT74L74 will behave as follows.
A. Loop-Timing (Uses the RxLineClk signal as the
Timing Reference)
Since the XRT74L74 is configured to operate in the
loop-timed mode, the Transmit Section (of the
XRT74L74) will use the RxLineClk input clock signal
(e.g., the Recovered Clock signal, from the LIU) as its
timing source. When the XRT74L74 is operating in
this mode it will do the following.
1. It will ignore any signal at the TxInClk input pin.
2. The XRT74L74 will output a 44.736MHz clock
signal via the RxOutClk output pin. This clock
signal functions as the Transmit Payload Data
Input Interface block clock signal.
3. The XRT74L74 will use the rising edge of the
RxOutClk signal to latch in the data residing on
the TxSer input pin.
B. Serial Mode
The XRT74L74 will accept the DS3 payload data from
the Terminal Equipment, in a serial-manner, via the
TxSer input pin The Transmit Payload Data Input In-
terface block will latch this data into its circuitry, on the
rising edge of the RxOutClk output clock signal.
C. Delineation of outbound DS3 frames
The XRT74L74 will pulse the TxFrame output pin
"High" for one bit-period coincident with the
XRT74L74 processing the last bit of a given DS3
frame.
D. Sampling of Payload Data, from the Terminal
Equipment
In Mode 1, the XRT74L74 will sample the data at the
TxSer input, on the rising edge of RxOutClk.
Interfacing the Transmit Payload Data Input Inter-
face block (of the XRT74L74) to the Terminal
Equipment for Mode 1 Operation
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