XR72L52 Datasheet, PDF (109/480 Pages) Exar Corporation – TWO CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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TWO CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
XRT72L52
REV. 1.0.1
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.
NOTE: 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 mes-
sage) 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.
NOTE: 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)
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 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)
NOTE: 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 proce-
dure.
NOTE: 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.
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.
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