XRT74L73 Datasheet, PDF (354/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
PRELIMINARY
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.
RXE3 INTERRUPT ENABLE REGISTER - 2 (ADDRESS = 0X13)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
Not Used
FERF
BIP-4 Error Framing Error
Interrupt Enable Interrupt Enable Interrupt Enable
R/W
RO
RO
RO
R/W
R/W
R/W
0
0
0
0
0
1
0
BIT 0
Not Used
RO
0
After doing this, the XRT74L73 Framer IC will gener-
ate 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 Trans-
mitter will transmit a LAPD Message to the Local Re-
ceiver via either the “N” bit within each E3 Frame.
The LAPD Receiver will receive and store the infor-
mation 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 respon-
sibilities.
• 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 149 .
355