XRT72L13 Datasheet, PDF (135/370 Pages) Exar Corporation – M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC

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PRELIMINARY
M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC XRT72L13
REV. 1.0.6
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 Trans-
mitter must be enabled before it can be commanded
to transmit a LAPD Message frame (containing a PM-
DL 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 _.
2.3.2.49 TxDS3 LAPD Status/Interrupt Register)
TXDS3 LAPD STATUS AND INTERRUPT REGISTER (ADDRESS = 0X34)
BIT 7
RO
0
BIT 6
BIT 5
Not Used
RO
RO
0
0
BIT 4
RO
0
BIT 3
TxDL Start
BIT 2
TxDL Busy
R/W
RO
0
0
BIT 1
TxLAPD
Interrupt
Enable
R/W
0
BIT 0
TxLAPD
Interrupt
Status
RUR
0
Bit 3 - TxDL Start
This "Read/Write" bit-field allows the user to invoke
the "Transmit LAPD Message" command. Once the
user invokes this command, the LAPD Transmitter will
do the following:
• Read in the PMDL Message from the "Transmit
LAPD Message" Buffer.
• Encapsulate the PMDL Message into a complete
LAPD Message frame by including the necessary
header and trailer bytes (e.g., flag sequence bytes,
SAPI, CR, EA values, etc.).
• 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.
• Proceed to transmit the LAPD Message Frame to
the "far end" terminal via the outgoing DS3 frames.
Writing a "1" to this bit-field start the transmission of
the LAPD Message Frame, via the LAPD Transmitter.
NOTE: For more information on the LAPD Transmitter,
please see Section _.
Bit 2 - TxDL Busy
This "Read-Only" bit-field allows the local µP to "poll"
and determine if the LAPD Transmitter has completed
its transmission of the LAPD Message frame. This
bit-field will contain a "1", if the LAPD Transmitter is
still transmitting the LAPD Message frame to the "far-
end" terminal. This bit-field will toggle to "0", once the
LAPD Transmitter has completed its transmission of
the LAPD Message frame.
NOTE: For more information on the LAPD Transmitter,
please see Section _.
Bit 1 - TxLAPD Interrupt Enable
This "Read/Write" bit-field allows the user to enable
or disable the "LAPD Message Frame Transmission
Complete" 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 indicates whether or
not the "LAPD Message frame Transmission Com-
plete" interrupt has occurred since the last read of
this register. The purpose of this interrupt is to let the
local µP know that the LAPD Transmitter has com-
pleted its transmission of the LAPD Message frame
(containing the latest PMDL message); and is now
ready to transmit another LAPD Message frame.
A "0" in this bit-field indicates that the "LAPD Mes-
sage frame Transmission Complete" interrupt has not
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