XRT7250 datasheet(157/463 Pages) EXAR

157 / 463 page

XRT7250

DS3/E3 FRAMER IC

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REV. 1.1.1

138

The XRT7250 will receive the DS3 payload data, in a

serial manner, via the TxSer input pin. The Transmit

Payload Data Input Interface (within the XRT7250)

will latch this data into its circuitry, on the rising edge

of the TxInClk input clock signal.

C. Delineation of outbound DS3 frames (Frame

Slave Mode)

The Transmit Section (of the XRT7250) will use the

TxInClk input as its timing reference, and will use the

TxFrameRef input signal as its framing reference. In

other words, the Transmit Section of the XRT7250 will

initiate frame generation upon the rising edge of the

TxFrameRef input signal).

D. Sampling of payload data, from the Terminal

Equipment

In Mode 2, the XRT7250 will sample the data, at the

TxSer input pin, on the rising edge of TxInClk.

Interfacing the Transmit Payload Data Input Inter-

face block (of the XRT7250) to the Terminal Equip-

ment for Mode 2 Operation

Figure 46 presents an illustration of the Transmit Pay-

load Data Input Interface block (within the XRT7250)

being interfaced to the Terminal Equipment, for Mode

2 operation.

Mode 2, Operation of the Terminal Equipment

As shown in Figure 46, both the Terminal Equipment

and the XRT7250 will be driven by an external

44.736MHz clock signal. The Terminal Equipment

will receive the 44.736MHz clock signal via its

DS3_Clock_In input pin, and the XRT7250 Framer IC

will receive the 44.736MHz clock signal via the TxIn-

Clk input pin.

The Terminal Equipment will serially output the pay-

load data of the outbound DS3 data stream, via the

DS3_Data_Out output pin, upon the rising edge of

the signal at the DS3_Clock_In input pin.

NOTE: The DS3_Data_Out output pin of the Terminal

Equipment is electrically connected to the TxSer input pin.

The XRT7250 Framer IC will latch the data, residing

on the TxSer input line, on the rising edge of the TxIn-

Clk signal.

In this case, the Terminal Equipment has the respon-

sibility of providing the framing reference signal by

pulsing its Tx_Start_of_Frame output signal (and in

turn, the TxFrameRef input pin of the XRT7250),

"High" for one-bit period, coincident with the first bit of

a new DS3 frame. Once the XRT7250 detects the

rising edge of the input at its TxFrameRef input pin, it

will begin generation of a new DS3 frame.

NOTES:

1. In this case, the Terminal Equipment is controlling

the start of Frame Generation, and is therefore

referred to as the Frame Master. Conversely, since

the XRT7250 does not control the generation of a

FIGURE 46. ILLUSTRATION OF THE TERMINAL EQUIPMENT BEING INTERFACED TO THE TRANSMIT PAYLOAD DATA

INPUT INTERFACE BLOCK OF THE XRT7250 FOR MODE 2 (SERIAL/LOCAL-TIMED/FRAME-SLAVE) OPERATION

Terminal Equipment

XRT7250 DS3 Framer

DS3_Data_Out

DS3_Clock_In

Tx_Start_of_Frame

DS3_Overhead_Ind

TxSer

TxInClk

TxFrameRef

TxOH_Ind

NibInt

44.736 MHz Clock

Source

XRT7250 Datasheet(PDF) 157 Page - Exar Corporation

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