XRT7250 Datasheet, PDF (121/463 Pages) Exar Corporation – DS3/E3 FRAMER IC

XRT7250 DS3/E3 FRAMER IC
REV. 1.1.1
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TXE3 LAPD CONFIGURATION REGISTER (ADDRESS = 0X33)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
Not Used
Auto Retrans- Not Used
mit
RO
RO
RO
RO
R/W
RO
0
0
0
0
1
0
BIT 1
TxLAPD
Msg Length
R/W
0
BIT 0
TxLAPD
Enable
R/W
0
Bit 3 - Auto Retransmit
This Read/Write bit-field allows the user to configure
the LAPD Transmitter to either transmit the LAPD
Message frame only once, or repeatedly at one-sec-
ond intervals.
Writing a "0" to this bit-field configures the LAPD
Transmitter to transmit the LAPD Message frame
once. Afterwards, the LAPD Transmitter will halt
transmission, until it has commanded to transmit an-
other LAPD Message frame.
Writing a "1" to this bit-field configures the LAPD
Transmitter to transmit the LAPD Message frame re-
peatedly at One-Second intervals. In this configura-
tion, the LAPD Transmitter will repeat its transmission
of the LAPD Message frame until it has been dis-
abled.
Bit 1 - TxLAPD Message Length Select
This Read/Write bit-field permits the user to select
the length of the outbound LAPD Message frame.
Setting this bit-field to "0" configures the outbound
LAPD Message frame to be 76 bytes in length. Set-
ting this bit-field to "1" configures the outbound LAPD
Message frame to be 82 bytes in length.
Bit 0 - TxLAPD Enable
This Read/Write bit-field allows the user to enable or
disable the LAPD Transmitter. The LAPD Transmitter
must be enabled before it can be commanded to
transmit a LAPD Message frame (containing a PMDL
message) via the outbound DS3 frames, to the Far-
End Terminal.
Writing a "0" disables the LAPD Transmitter (default
condition). Writing a "1" enables the LAPD Transmit-
ter.
NOTE: For information on the LAPD Transmitter, please see
Section 4.2.3.
2.3.7.3 Transmit E3 LAPD Status and Interrupt
Register (ITU-T G.751)
TXE3 LAPD STATUS AND INTERRUPT REGISTER (ADDRESS = 0X34)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Not Used
TXDL Start TXDL Busy
TxLAPD
Interrupt
Enable
TxLAPD
Interrupt
Status
RO
RO
RO
RO
R/W
RO
R/W
RUR
0
0
0
0
0
0
0
0
Bit 3 - TxDL Start
This Read/Write bit-field allows the user to command
the LAPD Transmitter to do the following.
• Scan through the PMDL Message, within the Trans-
mit LAPD Message buffer, and search for a string of
five (5) consecutive "1’s". The LAPD Transmitter
will then insert (or stuff) a "0" into the PMDL Mes-
sage data, immediately following any string of 5
consecutive "1’s".
• Read in this stuffed PMDL Message from the Trans-
mit LAPD Message buffer, and encapsulate it into a
LAPD Message frame.
• Fragment the resulting LAPD Message frame into
octets.
• Insert these octets into either the GC byte-field or
the NR byte-field (depending upon the user's selec-
tion) in each outbound E3 frame.
A "0" to "1" transition, in this bit-field commands the
LAPD Transmitter to initiate the above-mentioned
procedure.
NOTE: Once the user has commanded the LAPD Transmit-
ter to start transmission, the LAPD Transmitter will repeat
the above-mentioned process once each second and will
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