XRT7250 Datasheet, PDF (106/463 Pages) Exar Corporation – DS3/E3 FRAMER IC

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DS3/E3 FRAMER IC
XRT7250
REV. 1.1.1
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 3.2.3.2.
2.3.5.5 Transmit DS3 LAPD Status and Inter-
rupt Register (DS3 Applications)
TXDS3 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 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 3.2.3.2.
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 3.2.3.2.
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 Complete
interrupt has occurred since the last read of this reg-
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