XRT7250 datasheet(266/463 Pages) EXAR

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XRT7250

DS3/E3 FRAMER IC

REV. 1.1.1

247

indicate that it is processing the last nibble, within a

given E3 frame, by pulsing its TxNibFrame output pin

"High" for one TxNibClk clock period. When the Ter-

minal Equipment detects a pulse at its

Tx_Start_of_Frame input pin, it is expected to trans-

mit the first nibble, of the very next outbound E3

frame to the XRT7250 via the E3_Data_Out[3:0] (or

TxNib[3:0] pins).

Finally, for the Nibble-Parallel Mode operation, the

XRT7250 will pulse the TxOHInd output pin "High” for

3 nibble-periods (e.g., the 3 nibbles consisting of the

10 bit FAS pattern, the “A” and the “N” bits). The Tx-

OHInd output pin will remain "Low” for the remainder

of the frame period. The TxOHInd output pin will tog-

gle "High” one-nibble period before the Transmit Sec-

tion (of the Framer IC) processes the first four bits of

the FAS pattern.

The behavior of the signals between the XRT7250

and the Terminal Equipment for E3 Mode 4 Operation

is illustrated in Figure 107.

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

MENT

(MODE 4 OPERATION)

Terminal Equipment Signals

RxOutClk

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: TxNibFrame pulses high to denote

E3 Frame Boundary.

RxOutClk

TxNibFrame

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

0101

XRT7250 Datasheet(PDF) 266 Page - Exar Corporation

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