XRT7250 datasheet(330/463 Pages) EXAR

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XRT7250

DS3/E3 FRAMER IC

REV. 1.1.1

311

Table 64 relates the number of rising clock edges (in

the RxOHClk signal, since the RxOHFrame signal

was last sampled "High”) to the E3 Overhead bit that

is being output via the RxOH output pin.

Figure 146 presents the typical behavior of the Re-

ceive Overhead Data Output Interface block, when

Method 1 is being used to sample the incoming E3

overhead bits.

TABLE 63: LISTING AND DESCRIPTION OF THE PIN ASSOCIATED WITH THE RECEIVE OVERHEAD DATA OUTPUT

INTERFACE BLOCK (FOR METHOD 1)

SIGNAL NAME

TYPE

DESCRIPTION

RxOH

Output

Receive Overhead Data Output pin:

The XRT7250 will output the overhead bits, within the incoming E3 frames, via this pin.

The Receive Overhead Data Output Interface block will output a given overhead bit, upon the

falling edge of RxOHClk. Hence, the external data link equipment should sample the data, at

this pin, upon the rising edge of RxOHClk.

NOTE: The XRT7250 will always output the E3 Overhead bits via this output pin. There are no

external input pins or register bit settings available that will disable this output pin.

RxOHClk

Output

Receive Overhead Data Output Interface Clock Signal:

The XRT7250 will output the Overhead bits (within the incoming E3 frames), via the RxOH out-

put pin, upon the falling edge of this clock signal.

As a consequence, the user's data link equipment should use the rising edge of this clock sig-

nal to sample the data on both the RxOH and RxOHFrame output pins.

NOTE: This clock signal is always active.

RxOHFrame

Output

Receive Overhead Data Output Interface - Start of Frame Indicator:

The XRT7250 will drive this output pin "High” (for one period of the RxOHClk signal) whenever

the first overhead bit within a given E3 frame is being driven onto the RxOH output pin.

TABLE 64: THE RELATIONSHIP BETWEEN THE NUMBER OF RISING CLOCK EDGES IN RXOHCLK, (SINCE

RXOHFRAME WAS LAST SAMPLED "HIGH”) TO THE E3 OVERHEAD BIT, THAT IS BEING OUTPUT VIA THE RXOH

OUTPUT PIN

NUMBER OF RISING CLOCK EDGES IN RXOHCLK

THE OVERHEAD BIT BEING OUTPUT BY THE

XRT7250

0 (Clock edge is coincident with RxOHFrame being detected "High”)

FAS Pattern - Bit 9

FAS Pattern - Bit 8

FAS Pattern - Bit 7

FAS Pattern - Bit 6

FAS Pattern - Bit 5

FAS Pattern - Bit 4

FAS Pattern - Bit 3

FAS Pattern - Bit 2

FAS Pattern - Bit 1

FAS Pattern - Bit 0

A Bit

N Bit

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