XRT7250 datasheet(262/463 Pages) EXAR

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XRT7250

DS3/E3 FRAMER IC

REV. 1.1.1

243

Tx_Start_of_Frame (or TxFrameRef) signal is syn-

chronized to the TxInClk input clock signal.

Finally, the XRT7250 will pulse its TxOH_Ind output

pin, one bit-period prior to it processing a given over-

head bit, within the outbound E3 frame. Since the

TxOH_Ind output pin of the XRT7250 is electrically

connected to the E3_Overhead_Ind whenever the

XRT7250 pulses the TxOH_Ind output pin "High", it

will also be driving the E3_Overhead_Ind input pin (of

the Terminal Equipment) "High". Whenever the Ter-

minal Equipment detects this pin toggling "High", it

should delay transmission of the very next E3 frame

payload bit by one clock cycle.

The behavior of the signals between the XRT7250

and the Terminal Equipment for E3 Mode 2 Operation

is illustrated in Figure 103.

How to configure the XRT7250 to operate in this

mode.

1. Set the NibIntf input pin "Low".

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

Framer Operating Mode Register) to "01" as

depicted below.

3. Interface the XRT7250, to the Terminal Equip-

ment, as illustrated in Figure 102.

5.2.1.3

Mode 3 - The Serial/Local-Timed/

Frame-Master Mode Behavior of the XRT7250

FIGURE 103. BEHAVIOR OF THE TERMINAL INTERFACE SIGNALS BETWEEN THE XRT7250 AND THE TERMINAL

EQUIPMENT (MODE 2 OPERATION)

Terminal Equipment Signals

E3_Clock_In

E3_Data_Out

Tx_Start_of_Frame

E3_Overhead_Ind

XRT7250 Transmit Payload Data I/F Signals

TxInClk

TxSer

TxFrameRef

TxOH_Ind

Payload[1522]

Payload[1523]

FAS, Bit 9

FAS, Bit 8

Payload[1522]

Payload[1523]

FAS, Bit 9

FAS, Bit 8

Note: FAS Pattern bits will not be processed by the

Transmit Payload Data Input Interface.

E3 Frame Number N

E3 Frame Number N + 1

Note: TxFrame pulses high to denote

E3 Frame Boundary.

Note: TxOH_Ind pulses high for

12 bit periods in order to

denote Overhead Data

(e.g., the FAS pattern

and the A & N bits).

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) 262 Page - Exar Corporation

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