XRT72L13 Datasheet, PDF(257/370 Page) Exar Corporation – M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC

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XRT72L13 Datasheet, PDF (257/370 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

3. Interface the XRT72L13, to the Terminal Equip-

ment, as illustrated in Figure 69 .

NOTE: The XRT72L13 Framer IC cannot support the

âFramer Local Loop-backâ Mode of operation. The user

must configure the XRT72L13 Framer IC into any of the fol-

lowing modes, prior to configuring the âFramer Local-Loop-

backâ Mode operation.

â¢ Mode 2 - Serial/Local-Timed/Frame-Slave Mode.

â¢ Mode 3 - Serial/Local-Timed/Frame-Master Mode.

â¢ Mode 5 - Nibble-Parallel/Local-Timed/Frame-Slave

Mode.

â¢ Mode 6 - Nibble-Parallel/Local-Timed/Frame-Mas-

ter Mode.

For more detailed information on the âFramer Local

Loop-back Modeâ Operation, please see Section 6.0.

4.2.1.5 Mode 5 - The "Nibble-Parallel/Local-

Timed/Frame-Slave" Interface Mode

Behavior of the XRT72L13

If the XRT72L13 has been configured to operate in

this mode, then the XRT72L13 will function as fol-

lows:

A. Local-Timed (Uses the "TxInClk" signal as the

Timing Reference)

In this mode, the Transmit Section of the XRT72L13

will use the TxInClk signal at its timing reference.

Further, the chip will internally divide the "TxInClk"

clock signal by a factor of "4" and will output this divid-

ed clock signal via the "TxNibClk" output pin. The

"Transmit Terminal Equipment Input Interface" block

(within the XRT72L13) will use the rising edge of the

"TxNibClk" signal, to latch the data, residing on the

"TxNib[3:0] into its circuitry.

B. Nibble-Parallel Mode

The XRT72L13 will accept the "DS3 payload" data,

from the Terminal Equipment, in a parallel manner,

via the "TxNib[3:0]" input pins. The "Transmit Termi-

nal Equipment Input Interface" will latch this data into

its circuitry, on the rising edge of the "TxNibClk" out-

put signal.

C. Delineation of "outbound" DS3 Frames

The Transmit Section will use the "TxInClk" input sig-

nal as its timing reference; and will use the "Tx-

FrameRef" input signal as its "Framing Reference"

(e.g., the Transmit Section of the XRT72L13 initiates

frame generation upon the rising edge of the "Tx-

FrameRef" signal).

NOTE: In this case, the Terminal Equipment should pulse

the âTxFrameRefâ input signal (of the XRT72L13 Framer IC)

coincident with it applying the first payload nibble, within a

given âoutboundâ DS3 frame. Hence, the duration of this

pulse should be one ânibble-periodâ of the DS3 signal (see

Figure 33).

D. Sampling of payload data, from the Terminal

Equipment

In Mode 5, the XRT72L13 will sample the data, at the

"TxNib[3:0]" input pins, on the third rising edge of the

"TxInClk" clock signal, following a pulse in the "TxNib-

Clk" signal (see Figure 72 ).

NOTE: The "TxNibClk" signal, from the XRT72L13; oper-

ates nominally at 11.184 MHz (e.g., 44.736 MHz divided by

4). However, for reasons described below, "TxNibClk"

effectively operates at a lower clock frequency. The Trans-

mit Payload Data Input Interface is only used to accept the

payload data, which is intended to be carried by "outbound"

DS3 frames. The Transmit Payload Data Input Interface is

not designed to accommodate the entire DS3 data stream.

The DS3 Frame consists of 4704 payload bits or 1176

nibbles. Therefore, the XRT72L13 will supply 1176

"TxNibClk" pulses between the rising edges of two

consecutive "TxNibFrame" pulses. The DS3 Frame

repetition rate is 9.398kHz. Hence, 1176 "TxNibClk"

pulses for each DS3 frame period amounts to "TxNib-

Clk" running at approximately 11.052 MHz. The

method by which the 1176 "TxNibClk" pulses are dis-

tributed throughout the DS3 frame period is present-

ed below.

Nominally, the "Transmit Section" within the

XRT72L13 will generate a "TxNibClk" pulse for every

4 "RxOutClk" (or "TxInClk") periods. However, in 14

cases (within a DS3 frame period), the Transmit Pay-

load Data Input Interface will allow 5 "TxInClk" peri-

ods to occur between two consecutive "TxNibClk"

pulses.

Interfacing the "Transmit Payload Data Input In-

terface" block (of the XRT72L13) to the Terminal

Equipment for Mode 5 Operation

Figure 71 presents an illustration of the "Transmit

Payload Data Input Interface" block (within the

XRT72L13) being interfaced to the Terminal Equip-

ment, for "Mode 5" Operation.

245

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