XRT7250 datasheet(260/463 Pages) EXAR

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XRT7250

DS3/E3 FRAMER IC

REV. 1.1.1

241

How to configure the XRT7250 into the Serial/

Loop-Timed/Non-Overhead Interface Mode

1. Set the NibIntf input pin "Low".

2. Set the TimRefSel[1:0] bit fields (within the

Framer Operating Mode Register) to "00", as

illustrated below.

3. Interface the XRT7250, to the Terminal Equip-

ment, as illustrated in Figure 100.

5.2.1.2

Mode 2 - The Serial/Local-Timed/

Frame-Slave Mode Behavior of the XRT7250

If the XRT7250 has been configured to operate in this

mode, then the XRT7250 will function as follows.

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

Timing Reference

In this mode, the Transmit Section of the XRT7250

will use the TxInClk signal as its timing reference.

B. Serial Mode

The XRT7250 will receive the E3 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.

FIGURE 101. BEHAVIOR OF THE TERMINAL INTERFACE SIGNALS BETWEEN THE XRT7250 TRANSMIT PAYLOAD DATA

INPUT INTERFACE BLOCK AND THE TERMINAL EQUIPMENT (FOR MODE 1 OPERATION)

Terminal Equipment Signals

E3_Clock_In

E3_Data_Out

Tx_Start_of_Frame

E3_Overhead_Ind

XRT7250 Transmit Payload Data I/F Signals

RxOutClk

TxSer

TxFrame

TxOH_Ind

Payload[1522]

Payload[1523]

FAS, Bit 9

FAS, Bit 8

Payload[1522]

Payload[1523]

FAS, Bit 9

FAS, Bit 8

Note: The FAS pattern will not be processed by the

Transmit Payload Data Input Interface.

E3 Frame Number N

E3 Frame Number N + 1

Note: TxFrame pulses high to denote

E3 Frame Boundary.

Note: TxOH_Ind pulses high for

12 bit periods in order to

denote Overhead Data

(e.g., the FAS pattern and the

A & N bits).

FRAMER OPERATING MODE REGISTER (ADDRESS = 0X00)

BIT 7BIT 6BIT 5BIT 4BIT 3BIT2

BIT 1

BIT 0

Local

Loopback

DS3/E3*

Internal

LOS

Enable

RESET

Interrupt

Enable

Reset

Frame

Format

TimRefSel[1:0]

R/W

0101

XRT7250 Datasheet(PDF) 260 Page - Exar Corporation

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