XRT72L50
á
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
69
NOTE: For more information on the LAPD Receiver, refer to
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:
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
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 P 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 P 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)
This Read-Only register contains the value of the NR byte, within the most recently received E3 frame.
RXLAPDTYPE[1:0]
MESSAGE TYPE
MESSAGE LENGTH
0
CL Path Identification
76 Bytes
0
1
Idle Signal Identification
76 Bytes
1
0
Test Signal Identification
76 Bytes
1
ITU-T Path Identification
82 Bytes
RxE3 NR Byte Register (Address = 0x1A)
BIT 7BIT 6BIT 5BIT 4BIT 3BIT 2BIT 1BIT 0
RxNR[7:0]
RO
00
000