XRT7250 datasheet(322/463 Pages) EXAR

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XRT7250

DS3/E3 FRAMER IC

REV. 1.1.1

303

2. Enable the BIP-4 Error Interrupt. This is accom-

plished by writing a “1” into bit-field 2 (BIP-4 Error

Interrupt Enable) within the RxE3 Interrupt

Enable Register, as illustrated below.

After doing this, the XRT7250 Framer IC will generate

an interrupt to the Microprocessor/Microcontroller

anytime the Receive Section detects a BIP-4 error.

5.3.3

The Receive HDLC Controller Block

The Receive E3 HDLC Controller block can be used

to receive message-oriented signaling (MOS) type

data link messages from the remote terminal equip-

ment.

The MOS types of HDLC message processing is dis-

cussed in detail below.

The Message Oriented Signaling (e.g., LAP-D)

Processing via the Receive E3 HDLC Controller

block

The LAPD Receiver (within the Receive E3 HDLC

Controller block) allows the user to receive PMDL

messages from the remote terminal equipment, via

the inbound E3 frames. In this case, the inbound

message bits will be carried by the “N” bit-field within

each inbound E3 Frame. The remote LAPD Transmit-

ter will transmit a LAPD Message to the Local Receiv-

er via either the “N” bit within each E3 Frame. The

LAPD Receiver will receive and store the information

portion of the received LAPD frame into the Receive

LAPD Message Buffer, which is located at addresses:

0xDE through 0x135 within the on-chip RAM. The

LAPD Receiver has the following responsibilities.

• Framing to the incoming LAPD Messages

• Filtering out stuffed "0’s" (within the information

payload)

• Storing the Frame Message into the Receive LAPD

Message Buffer

• Perform Frame Check Sequence (FCS) Verification

• Provide status indicators for

End of Message (EOM)

Flag Sequence Byte detected

Abort Sequence detected

Message Type

C/R Type

The occurrence of FCS Errors

The LAPD receiver's actions are facilitated via the fol-

lowing two registers.

• Rx E3 LAPD Control Register

• Rx E3 LAPD Status Register

Operation of the LAPD Receiver

The LAPD Receiver, once enabled, will begin search-

ing for the boundaries of the incoming LAPD mes-

sage. The LAPD Message Frame boundaries are de-

lineated via the Flag Sequence octets (0x7E), as de-

picted in Figure 142.

RXE3 INTERRUPT ENABLE REGISTER - 2 (ADDRESS = 0X13)

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

Not Used

FERF

Interrupt Enable

BIP-4 Error

Interrupt Enable

Framing Error

Interrupt Enable

Not Used

R/W

000

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