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XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
92
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 another LAPD
Message frame.
Writing a "1" to this bit-field configures the LAPD Transmitter to transmit the LAPD Message frame repeatedly
at One-Second intervals. In this configuration, the LAPD Transmitter will repeat its transmission of the LAPD
Message frame until it has been disabled.
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. Setting this
bit-field to "1" configures the outbound LAPD Message frame to be 82 bytes in length.
N
OTE
:
This should match with the message type of the LAPD message to be sent. (See
Table 21
.)
Bit 0 - TxLAPD Enable
This Read/Write bit-field permits 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 E3 frames, to the Remote Terminal.
Writing a "0" disables the LAPD Transmitter (default condition). Writing a "1" enables the LAPD Transmitter.
N
OTE
:
For information on the LAPD Transmitter, refer to
Section 6.2.3.1
.
2.3.6.3
Transmit E3 LAPD Status and Interrupt Register (E3, ITU-T G.832)
Bit 3 - TxDL Start
This Read/Write bit-field permits the user to command the LAPD Transmitter to do the following.
Read in the PMDL Header and Message from the Transmit LAPD Message Buffer. (80 or 86 bytes)
Compute the frame check sequence word (16 bit value)
Insert the Frame Check Sequence value into the 2 octet slot after the payload section of the Message.
Perform zero stuffing between 0x7E flag bytes. (81 or 87 bytes)
N
OTE
:
Zero Stuffing: search for a string of five (5) consecutive "1’s" insert (or stuff) a "0" immediately following any string of
5 consecutive "1’s".
Proceed to transmit the LAPD Message Frame to the far end terminal via the outgoing DS3 frames.
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 selection)
into each outbound E3 frame.
A "0" to "1" transition, in this bit-field commands the LAPD Transmitter to initiate the above-mentioned
procedure.
N
OTE
:
Once the user has commanded the LAPD Transmitter to start transmission, the LAPD Transmitter will repeat the
above-mentioned process once each second and will insert flag sequence octets into the outbound LAPD channel,
during the idle periods between transmissions.
TxE3 LAPD Status and Interrupt Register (Address = 0x34)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
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