XRT7250 datasheet(261/463 Pages) EXAR

261 / 463 page

XRT7250

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DS3/E3 FRAMER IC

REV. 1.1.1

242

C. Delineation of outbound E3 frames (Frame

Slave Mode)

The Transmit Section of the XRT7250 will use the Tx-

InClk 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 102 presents an illustration of the Transmit

Payload Data Input Interface block (within the

XRT7250) being interfaced to the Terminal Equip-

ment, for Mode 2 operation.

Mode 2 Operation of the Terminal Equipment

As shown in Figure 102, both the Terminal Equipment

and the XRT7250 will be driven by an external

34.368MHz clock signal. The Terminal Equipment

will receive the 34.368MHz clock signal via its

E3_Clock_In input pin, and the XRT7250 Framer IC

will receive the 34.368MHz clock signal via the TxIn-

Clk input pin.

The Terminal Equipment will serially output the pay-

load data of the outbound E3 data stream, via the

E3_Data_Out output pin, upon the rising edge of the

signal at the E3_Clock_In input pin.

NOTE: The E3_Data_Out output pin of the Terminal Equip-

ment 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 E3 frame. Once the XRT7250 detects the ris-

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

will begin generation of a new E3 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

new E3 frame, but is rather driven by the Terminal

Equipment, the XRT7250 is referred to as the

Frame Slave.

2. If the user opts to configure the XRT7250 to oper-

ate in Mode 2, it is imperative that the

FIGURE 102. 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 E3 Framer

E3_Data_Out

E3_Clock_In

Tx_Start_of_Frame

E3_Overhead_Ind

TxSer

TxInClk

TxFrameRef

TxOH_Ind

NibInt

34.368 MHz Clock

Source

XRT7250 Datasheet(PDF) 261 Page - Exar Corporation

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