XRT7250 datasheet(165/463 Pages) EXAR

165 / 463 page

XRT7250

DS3/E3 FRAMER IC

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REV. 1.1.1

146

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 52.

4.2.1.6

Mode 6 - The Nibble-Parallel/TxInClk/

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 53. BEHAVIOR OF THE TERMINAL INTERFACE SIGNALS BETWEEN THE XRT7250 AND THE TERMINAL EQUIP-

MENT

(DS3 MODE 5 OPERATION)

Terminal Equipment Signals

XRT7250 Transmit Payload Data I/F Signals

DS3 Frame Number N

DS3 Frame Number N + 1

Note: TxFrameRef is pulsed high to denote

first nibble within a new DS3 frame

TxInClk

Tx_Start_of_Frame

DS3_Nib_Clock_In

DS3_Data_Out[3:0]

Nibble [0]

Nibble [1]

TxInClk

TxFrameRef

TxNibClk

TxNib[3:0]

Nibble [0]

Nibble [1]

Nibble [1175]

Sampling edge of the XRT7250

Device

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) 165 Page - Exar Corporation

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