XRT72L56 Datasheet, PDF (119/486 Pages) Exar Corporation – SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
PRELIMINARY
XRT72L56
REV. P1.1.2
Bit 6 - RxAbort
This Read-Only bit-field indicates whether or not the
LAPD Receiver is currently detecting an abort se-
quence (e.g., a string of 7 consecutive "1’s").
This bit-field is set to "1" if the LAPD Receiver is cur-
rently detecting an abort sequence in the incoming
LAPD Channel. Conversely, this bit-field is set to "0"
if the LAPD Receiver has not detected an abort se-
quence, since the last read of this register.
Bit 5, 4 - RxLAPD Type[1:0]
These two Read-Only bit-fields combine to indicate
the type and size of LAPD Message frame that has
been received by the LAPD Receiver. The following
table relates the contents of these bit-fields to the
LAPD Message type/size.
RXLAPDTYPE[1:0]
LAPD MESSAGE FRAME TYPE
PMDL MESSAGE SIZE (INFORMATION
SECTION)
00
CL Path Identification Type
76 Bytes
01
Idle Signal Identification Type
76 Bytes
10
Test Signal Identification Type
76 Bytes
11
ITU-T Path Identification Type
82 Bytes
Bit 3 - RxCR Type
This Read-Only bit-field indicates the state of the C/R
bit-field, within octet # 2 of the most recently received
LAPD Message frame.
Bit 2 - RxFCS Error
This Read-Only bit-field indicates whether or not the
LAPD Receiver has detected an FCS (Frame Check
Sequence) error, in the most recently received LAPD
Message frame. This bit-field is set to "0" if the LAPD
Receiver does not detect an FCS error in this LAPD
Message frame. Conversely, this bit-field is set to "1"
if the LAPD Receiver does detect an FCS error in this
LAPD Message frame.
NOTE: For a more detailed discussion on the LAPD
Receiver's handling of the FCS bytes, please see Section
4.3.3.
Bit 1 - EndOfMessage
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 con-
tains a new PMDL message that needs to be read
and processed.
This bit-field is cleared (to "0") upon reading this reg-
ister.
Bit 0 - Flag Present
The LAPD Receiver will assert this read-only bit-field
when it is currently detecting the Flag Sequence octet
(0x7E) 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 in-
coming LAPD channel.
2.4.4.9 Receive E3 Service Bits Register (E3,
ITU-T G.751)
RXE3 SERVICE BIT REGISTER (ADDRESS = 0X1A)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Not Used
RxA
RxN
RO
RO
RO
RO
RO
RO
RO
RO
0
0
0
0
0
0
0
0
Bit 1 - RxA (A-Bit)
This Read-Only bit-field reflects the state of the “A”
bit-field, within the most recently received E3 frame.
Bit 0 - RxN (N-Bit)
This Read-Only bit-field reflects the state of the “N”
bit-field, within the most recently received E3 frame.
2.4.5 Transmit DS3 Configuration Registers
2.4.5.1 Transmit DS3 Configuration Register
(DS3 Applications)
100