XRT7250 datasheet(167/463 Pages) EXAR

167 / 463 page

XRT7250

DS3/E3 FRAMER IC

áç

REV. 1.1.1

148

The Terminal Equipment will serially output the data

on the DS3_Data_Out[3:0] pins upon the rising edge

of the signal at the DS3_Clock_In input pin. The

XRT7250 will latch the data, residing on the Tx-

Nib[3:0] input pins, on the rising edge of the TxNibClk

signal.

In this case the XRT7250 has the responsibility of

providing the framing reference signal by pulsing the

TxFrame output pin (and in turn the

Tx_Start_of_Frame input pin of the Terminal Equip-

ment) "High" for one bit-period, coincident with the

last bit within a given DS3 frame.

Finally, the XRT7250 will always internally generate

the Overhead bits, when it is operating in both the

DS3 and Nibble-parallel modes. The XRT7250 will

pull the TxOHInd input pin "Low".

The behavior of the signals between the XRT7250

and the Terminal Equipment for DS3 Mode 6 Opera-

tion is illustrated in Figure 55.

How to configure the XRT7250 into Mode 6

1. Set the NibInt input pin "High".

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

Framer Operating Mode Register) to 1X as illus-

trated below.

FIGURE 55. BEHAVIOR OF THE TERMINAL INTERFACE SIGNALS BETWEEN THE XRT7250 AND THE TERMINAL EQUIP-

MENT

(DS3 MODE 6 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.

TxInClk

Tx_Start_of_Frame

DS3_Nib_Clock_In

DS3_Data_Out[3:0]

Nibble [1175]

Nibble [0]

TxInClk

TxNibFrame

TxNibClk

TxNib[3:0]

Nibble [1175]

Nibble [0]

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) 167 Page - Exar Corporation

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