XRT72L56 Datasheet, PDF (139/486 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
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 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 Transmit-
ter.
NOTE: For information on the LAPD Transmitter, please see
Section 4.2.3.
2.4.7.3 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 permits the user to com-
mand 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
insert flag sequence octets into the outbound LAPD chan-
nel, during the idle periods between transmissions.
Bit 2 - TxDL Busy
This Read-Only bit-field permits the user to poll or
monitor the status of the LAPD Transmitter to see if it
has completed its transmission of the LAPD Message
frame. The LAPD Transmitter will set this bit-field to
"1", while it is in the process of transmitting the LAPD
Message frame. However, the LAPD Transmitter will
clear this bit-field to "0" once it has completed its
transmission of the LAPD Message frame.
Bit 1 - TxLAPD Interrupt Enable
This Read/Write bit-field permits the user to enable or
disable the LAPD Message frame Transmission Com-
plete interrupt.
Writing a "0" to this bit-field disables this interrupt.
Writing a "1" to this bit-field enables this interrupt.
Bit 0 - TxLAPD Interrupt Status
This Reset-upon-Read bit-field permits the user to
determine if the LAPD Message Frame Transmission
Complete interrupt has occurred since the last read of
this register. If this bit-field contains a "1" then the
LAPD Message Frame Transmission Complete inter-
rupt has occurred since the last read of this register.
Conversely, if this bit-field contains a "0" then it has
not.
2.4.7.4 Transmit E3 Service Bits Register (ITU-
T G.751)
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