XRT7250 datasheet(257/463 Pages) EXAR

257 / 463 page

XRT7250

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DS3/E3 FRAMER IC

REV. 1.1.1

238

• The Serial or the Nibble-Parallel Interface Mode

• The Loop-Timing or the TxInClk (Local Timing)

Mode

Further, if the XRT7250 has been configured to oper-

ate in the Local-Timing mode, then the user has two

additional options.

• The XRT7250 is the Frame Master (e.g., it dictates

when the Terminal Equipment will initiate the trans-

mission of data within a new E3 frame).

• The XRT7250 is the Frame Slave (e.g., the Termi-

nal Equipment will dictate when the XRT7250 ini-

tiates the transmission of a new E3 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 XRT7250

If the XRT7250 has been configured to operate in this

mode, then the XRT7250 will behave as follows.

A. Loop-Timing (Uses the RxLineClk signal as the

Timing Reference)

Since the XRT7250 is configured to operate in the

loop-timed mode, the Transmit Section of the

XRT7250 will use the RxLineClk input clock signal

(e.g., the Recovered Clock signal, from the LIU) as its

timing source. When the XRT7250 is operating in this

mode it will do the following.

1. It will ignore any signal at the TxInClk input pin.

2. The XRT7250 will output a 34.368MHz clock sig-

nal via the RxOutClk output pin. This clock signal

functions as the Transmit Payload Data Input

Interface block clock signal.

3. The XRT7250 will use the rising edge of the

RxOutClk signal to latch in the data residing on

the TxSer input pin.

B. Serial Mode

The XRT7250 will accept the E3 payload data from

the Terminal Equipment, in a serial-manner, via the

TxSer input pin The Transmit Payload Data Input In-

terface will latch this data into its circuitry, on the ris-

ing edge of the RxOutClk output clock signal.

C. Delineation of outbound E3 frames

The XRT7250 will pulse the TxFrame output pin

"High" for one bit-period coincident with the XRT7250

processing the last bit of a given E3 frame.

D. Sampling of Payload Data, from the Terminal

Equipment

In Mode 1, the XRT7250 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 XRT7250 to the Terminal Equip-

ment for Mode 1 Operation

Figure 100 presents an illustration of the Transmit

Payload Data Input Interface block (within the

XRT7250) being interfaced to the Terminal Equip-

ment, for Mode 1 operation.

FIGURE 100. ILLUSTRATION OF THE TERMINAL EQUIPMENT BEING INTERFACED TO THE TRANSMIT PAYLOAD DATA

INPUT INTERFACE BLOCK OF THE XRT7250 FOR MODE 1 (SERIAL/LOOP-TIMED) OPERATION

Terminal Equipment

XRT7250 E3 Framer

E3_Data_Out

E3_Clock_In

Tx_Start_of_Frame

E3_Overhead_Ind

TxSer

RxOutClk

TxFrame

TxOH_Ind

NibInt

34.368 MHz

XRT7250 Datasheet(PDF) 257 Page - Exar Corporation

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