XRT72L50 Datasheet, PDF (389/471 Pages) Exar Corporation – SINGLE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
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TxE3 LAPD Configuration Register (Address = 0x33)
BIT 7
RO
0
BIT 6
BIT 5
Not Used
RO
RO
0
0
BIT 4
RO
0
BIT 3
Auto
Retransmit
R/W
1
BIT 2
Not Used
RO
0
BIT 1
TxLAPD
Msg Length
R/W
0
BIT 0
TxLAPD
Enable
R/W
0
If the user writes a “1” into this bit-field, then the LAPD Transmitter will transmit the LAPD Message frame
repeatedly at One-Second intervals until the LAPD Transmitter is disabled.
If the user writes a “0” into this bit-field, then the LAPD Transmitter will transmit the LAPD Message frame only
once. Afterwards, the LAPD Transmitter will halt its transmission until the user invokes the Transmit LAPD
Message frame command, once again.
STEP 6 - Enabling the LAPD Transmitter
Prior to the transmission of any data via the LAPD Transmitter, the LAPD Transmitter must be enabled by
writing a "1" to bit 0 (TxLAPD Enable) of the Tx E3 LAPD Configuration Register, as depicted below.
Transmit E3 LAPD Configuration Register (Address = 0x33)
BIT 7
RO
0
BIT 6
BIT 5
Not Used
RO
RO
0
0
BIT 4
RO
0
BIT 3
Auto
Retransmit
R/W
X
BIT2
Not Used
RO
0
BIT 1
TxLAPD
Msg Length
R/W
X
BIT 0
TxLAPD
Enable
R/W
1
If the user writes a “1” into this bit-field, then the LAPD Transmitter will be enabled, and the LAPD Transmitter
will immediately begin to transmit a continuous stream of Flag Sequence octets (0x7E), via either the GC or the
NR byte-field of each Outbound E3 frame (depending upon which byte has been selected to carry the PMDL
channel).
Conversely, if the user writes a “0” into this bit-field, then the LAPD Transmitter will be disabled. The Transmit
E3 Framer block will insert the contents of the Tx GC Byte Register into the GC byte-field for each Outbound
E3 frame. Likewise, the Transmit E3 Framer block will also insert the contents of the Tx NR Byte Register into
the NR” byte-field for each Outbound E3 frame. No transmission of PMDL data will occur.
STEP 7 - Initiate the Transmission
At this point, the user should have written the PMDL message into the on-chip Transmit LAPD Message buffer
and should have specified the type of LAPD Message that is to be transmitted. The user should have also
specified whether the LAPD Transmitter will transport the LAPD Message frame octets via the GC-byte field or
via the NR-byte field of each Outbound E3 frame. Finally the LAPD Transmitter should have been enabled.
Then initiate the transmission of this message by writing a “1” to Bit 3 (Tx DL Start) within the Tx E3 LAPD
Status and Interrupt Register (Address = 0x34), as depicted below.
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