XRT7250 datasheet(269/463 Pages) EXAR

269 / 463 page

XRT7250

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DS3/E3 FRAMER IC

REV. 1.1.1

250

How to configure the XRT7250 into Mode 5

1. Set the NibIntf input pin "High".

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

Framer Operating Mode Register) to "01" as illus-

trated below.

3. Interface the XRT7250, to the Terminal Equip-

ment, as illustrated in Figure 108.

5.2.1.6

4.2.1.6 Mode 6 - The Nibble-Parallel/

Local-Timed/Frame-Master Interface 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 at its timing reference.

Further, the chip will internally divide the TxInClk

clock signal by a factor of 4 and will output this divid-

ed clock signal via the TxNibClk output pin. The

Transmit Terminal Equipment Input Interface block

(within the XRT7250) will use the rising edge of the

TxNibClk signal, to latch the data, residing on the Tx-

Nib[3:0] into its circuitry.

FIGURE 109. BEHAVIOR OF THE TERMINAL INTERFACE SIGNALS BETWEEN THE XRT7250 AND THE TERMINAL

EQUIPMENT (E3, MODE 5 OPERATION)

Terminal Equipment Signals

TxInClk

Tx_Start_of_Frame

E3_Nib_Clock_In

E3_Data_Out[3:0]

Payload Nibble [380]

Overhead Nibble [0]

XRT7250 Transmit Payload Data I/F Signals

E3 Frame Number N

E3 Frame Number N + 1

Note: Terminal Equipment pulses

“TxFrameRef” in order to denote

the E3 Frame Boundary.

TxInClk

TxFrameRef

TxNibClk

TxNib[3:0]

Nibble [380]

Overhead Nibble [0]

E3_Overhead_Ind

TxOH_Ind

TxOH_Ind pulses high for 3 Nibble periods

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

101

XRT7250 Datasheet(PDF) 269 Page - Exar Corporation

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