XRT7250 datasheet(318/463 Pages) EXAR

318 / 463 page

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XRT7250

DS3/E3 FRAMER IC

REV. 1.1.1

299

5.3.2.10 Error Checking of the Incoming E3

Frames

The Receive E3 Framer block can be configured to

performs error-checking on the incoming E3 frame

data that it receives from the Remote Terminal Equip-

ment. If configured accordingly, the Receive E3

Framer block will performs this error-checking by

computing the BIP-4 value of an incoming E3 frame.

Once the Receive E3 Framer block has obtained this

value, it will compare this value with that of the BIP-4

value that it receives, within the very next E3 frame. If

the locally computed BIP-4 value matches the EM

byte of the corresponding E3 frame, then the Receive

E3 Framer block will conclude that this particular

frame has been properly received. The Receive E3

Framer block will then inform the Remote Terminal

Equipment of this fact by having the Local Terminal

Equipment Transmit E3 Framer block send the Re-

mote Terminal an E3 frame, with the “A” bit-field, set

to “0”.

This procedure is illustrated in Figure 138 and

Figure 139, below.

Figure 138 illustrates the Local Receive E3 Framer

receiving an error-free E3 frame. In this figure, the lo-

cally computed BIP-4 value of “0xA” matches that re-

ceived from the Remote Terminal, within the EM byte-

field. Figure 139 illustrates the subsequent action of

the Local Transmit E3 Framer block, which will trans-

mit an E3 frame, with the A bit-field set to “0”, to the

Remote Terminal. This signaling indicates that the

Local Receive E3 Framer has received an error-free

E3 frame.

RXE3 CONFIGURATION & STATUS REGISTER - 2 (ADDRESS = 0X11)

BIT 7BIT 6BIT 5BIT 4BIT 3BIT 2BIT 1BIT 0

RxLOF

Algo

RxLOF

RxOOF

RxLOS

RxAIS

Not Used

RxFERF

R/W

RORO

RORORORO

1100

111

FIGURE 138. ILLUSTRATION OF THE LOCAL RECEIVE E3 FRAMER BLOCK, RECEIVING AN E3 FRAME (FROM THE

REMOTE TERMINAL) WITH A CORRECT BIP-4 VALUE.

Transmit E3

Framer

Receive E3

Framer

Local Terminal

Remote

Terminal

BIP-4 Nibble

Locally Calculated

BIP-4 Nibble

0xA

XRT7250 Datasheet(PDF) 318 Page - Exar Corporation

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