XRT72L13 Datasheet, PDF (247/370 Pages) Exar Corporation – M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC

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PRELIMINARY
XRT72L13
M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC
REV. P1.0.6
TABLE 12: LISTING AND DESCRIPTION OF THE PINS ASSOCIATED WITH THE "TRANSMIT PAYLOAD DATA INPUT
INTERFACE
SIGNAL NAME TYPE
DESCRIPTION
RxOutClk
Output Loop-Timed Timing Reference Clock Output pin:
The Transmit Section of the XRT72L13 can be configured to use the "RxLineClk" signal as the
"Timing Reference" (e.g., loop-timing). If the user has made this configuration selection, then
the XRT72L13 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 user to make the
following configuration options.
• The "Serial" or the "Nibble-Parallel" Interface Mode
• The "Loop-Timing" or the "TxInClk" (Local Timing)
Mode
Further, if the XRT72L13 has been configured to op-
erate in the "TxInClk" (Local Timing) mode, then the
user has two additional options.
• The XRT72L13 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 XRT72L13 functions as the "Frame Slave"
(e.g., the Terminal Equipment will dictate when the
XRT72L13 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.
4.2.1.1 Mode 1 - The "Serial/Loop-Timing"
Mode
The Behavior of the XRT72L13
If the XRT72L13 has been configured to operate in
this mode, then the XRT72L13 will behave as follows.
A. Loop-Timing (Uses the "RxLineClk" signal as
the Timing Reference)
Since the XRT72L13 is configured to operate in the
"loop-timed" mode, the Transmit Section (of the
XRT72L13) will use the "RxLineClk" input clock signal
(e.g., the Recovered Clock signal, from the LIU) as its
timing source. When the XRT72L13 is operating in
this mode it will do the following.
1. It will ignore any signal at the "TxInClk" input pin.
2. The XRT72L13 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 XRT72L13 will use the rising edge of the
"RxOutClk" signal to latch in the data residing on
the TxSer input pin.
B. Serial Mode
The XRT72L13 will accept the "DS3" payload data
from the Terminal Equipment, in a serial-manner, via
the "TxSer" input pin The "Transmit Payload Data In-
put Interface" block will latch this data into its circuitry,
on the rising edge of the "RxOutClk" output clock sig-
nal.
C. Delineation of "outbound" DS3 frames
The XRT72L13 will pulse the "TxFrame" output pin
"high" for one bit-period; coincident with the
XRT72L13 processing the last bit of a given DS3
frame.
D. Sampling of Payload Data, from the Terminal
Equipment
In Mode 1, the XRT72L13 will sample the data at the
"TxSer" input, on the rising edge of "RxOutClk".
Interfacing the "Transmit Payload Data Input In-
terface" block (of the XRT72L13) to the Terminal
Equipment for Mode 1 Operation
Figure 63 presents an illustration of the "Transmit
Payload Data Input Interface" block (within the
XRT72L13) being interfaced to the Terminal Equip-
ment, for "Mode 1" operation.
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