XRT7250 datasheet(156/463 Pages) EXAR

156 / 463 page

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DS3/E3 FRAMER IC

XRT7250

REV. 1.1.1

137

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 44.

NOTE: The XRT7250 Framer IC cannot support the Framer

Local Loop-back Mode of operation, when operating in the

Loop-Timing Mode. The user must configure the XRT7250

Framer IC into any of the following modes, prior to configur-

ing the Framer Local Loop-back Mode.

• Mode 2 - Serial/Local-Timed/Frame-Slave Mode.

• Mode 3 - Serial/Local-Timed/Frame-Master Mode.

• Mode 5 - Nibble-Parallel/Local-Timed/Frame-Slave

Mode.

• Mode 6 - Nibble-Parallel/Local-Timed/Frame-Mas-

ter Mode.

For more detailed information on Framer Local Loop-

back Mode of operation, please see Section 6.0.

4.2.1.2

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-Timing - 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

FIGURE 45. BEHAVIOR OF THE TERMINAL INTERFACE SIGNALS BETWEEN THE TRANSMIT PAYLOAD DATA INPUT

INTERFACE BLOCK OF THE XRT7250 AND THE TERMINAL EQUIPMENT (FOR MODE 1 OPERATION)

Terminal Equipment Signals

DS3_Clock_In

DS3_Data_Out

Tx_Start_of_Frame

DS3_Overhead_Ind

XRT7250 Transmit Payload Data I/F Signals

RxOutClk

TxSer

TxFrame

TxOH_Ind

Payload[4702]

Payload[4703]

X-Bit

Payload[0]

Payload[4702]

Payload[4703]

X-Bit

Payload[0]

Note: X-Bit will not be processed by the

Transmit Payload Data Input Interface.

DS3 Frame Number N

DS3 Frame Number N + 1

Note: TxFrame pulses high to denote

DS3 Frame Boundary.

Note: TxOH_Ind pulses high to

denote Overhead Data

(e.g., the X-bit).

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

XRT7250 Datasheet(PDF) 156 Page - Exar Corporation

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