XRT7250 datasheet(162/463 Pages) EXAR

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DS3/E3 FRAMER IC

XRT7250

REV. 1.1.1

143

edge of the TxNibClk output clock signal. The

XRT7250 will indicate that it is processing the last

nibble, within a given DS3 frame, by pulsing its TxNib-

Frame output pin "High" for one TxNibClk clock peri-

od. When the Terminal Equipment detects a pulse at

its Tx_Start_of_Frame input pin, it is expected to

transmit the first nibble, of the very next outbound

DS3 frame to the XRT7250 via the

DS3_Data_Out[3:0] (or TxNib[3:0] pins).

Finally, for the Nibble-Parallel Mode operation, the

XRT7250 will continuously pull the TxOHInd output

pin "Low".

The behavior of the signals between the XRT7250

and the Terminal Equipment for DS3 Mode 4 Opera-

tion is illustrated in Figure 51.

How to configure the XRT7250 into Mode 4

1. Set the NibIntf input pin "High".

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

Framer Operating Mode Register) to “00" as illus-

trated below.

FIGURE 51. BEHAVIOR OF THE TERMINAL INTERFACE SIGNALS BETWEEN THE XRT7250 AND THE TERMINAL EQUIP-

MENT

(MODE 4 OPERATION)

Terminal Equipment Signals

XRT7250 Transmit Payload Data I/F Signals

DS3 Frame Number N

DS3 Frame Number N + 1

Note: TxNibFrame pulses high to denote

DS3 Frame Boundary.

RxOutClk

Tx_Start_of_Frame

DS3_Nib_Clock_In

DS3_Data_Out[3:0]

Nibble [1175]

Nibble [0]

RxOutClk

TxNibFrame

TxNibClk

TxNib[3:0]

Nibble [1175]

Nibble [0]

Sampling Edge of 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) 162 Page - Exar Corporation

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