XRT72L50 Datasheet, PDF (82/471 Pages) Exar Corporation – SINGLE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
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NOTE: For more information on the LAPD Receiver, refer to Section 4.3.3.2.
Bits, 5 and 4 - RxLAPDType[1:0]
These two Read Only bit-fields combine to indicate the type of LAPD Message frame that has been received
by the LAPD Receiver. The relationship between these two bit-fields and the LAPD Message Type follows:
RXLAPDTYPE[1:0]
MESSAGE TYPE
MESSAGE LENGTH
0
0
CL Path Identification
76 Bytes
0
1
Idle Signal Identification
76 Bytes
1
0
Test Signal Identification
76 Bytes
1
1
ITU-T Path Identification
82 Bytes
Bit 3 - RxCR (Command/Response) Type
This Read Only bit field indicates the value of the C/R (Command/Response) bit-field of the latest received
LAPD Message.
Bit 2 - Rx FCS (Frame Check Sequence) Error
This Read-Only bit-field indicates whether or not the LAPD Receiver has detected a Frame Check Sequence
(FCS) error in the most recently received LAPD Message Frame. A "0" in this bit-field indicates that the FCS
for the latest received LAPD Message Frame is correct. A "1" in this bit-field indicates that the FCS for the
latest received LAPD Message Frame is incorrect.
NOTE: For more information on the LAPD Receiver, refer to Section 4.3.3.2.
Bit 1 - End Of Message
This Read-Only bit-field indicates whether or not the LAPD Receiver has completed its reception of the latest
incoming LAPD Message frame. The local µP can poll the progress of the LAPD Receiver by periodically
reading this bit-field.
The LAPD Receiver will assert this read-only bit-field, when it has received a complete LAPD Message frame.
This bit-field, along with the Receipt of New LAPD Message frame interrupt, serves to inform the local µP that
the Receive LAPD Message buffer contains a new PMDL message that needs to be read and processed.
This bit-field is cleared (to "0") when the LAPD receiver starts receiving a new LAPD frame. (The EOM bit goes
“Low” once a valid header is received.).
A "0" in this bit-field indicates that the LAPD Receiver is still receiving the latest message from the remote
LAPD Transmitter. A "1" in this bit-field indicates that the LAPD Receiver has finished receiving the complete
LAPD Message Frame.
Bit 0 - Flag Present
The LAPD Receiver will assert this read-only bit-field when it is currently detecting the Flag Sequence octet
(7Eh) in the incoming LAPD channel (e.g., either the GC or the NR byte-field, within each E3 frame). The
LAPD Receiver will negate this bit-field when it is no longer receiving the Flag Sequence octet in the incoming
LAPD channel.
2.3.3.9 Receive E3 NR Byte Register (E3, ITU-T G.832)
RxE3 NR Byte Register (Address = 0x1A)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
RxNR[7:0]
RO
RO
RO
RO
RO
RO
RO
RO
0
0
0
0
0
0
0
0
This Read-Only register contains the value of the NR byte, within the most recently received E3 frame.
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