XRT74L73 Datasheet, PDF (415/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

PRELIMINARY
XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
TABLE 93: RELATIONSHIP BETWEEN TXLAPD MSG LENGTH AND THE LAPD MESSAGE SIZE
TXLAPD MESSAGE LENGTH
LAPD MESSAGE LENGTH
0
LAPD Message size is 76 bytes
1
LAPD Message size is 82 bytes
NOTE: The Message Type selected must correspond with
the contents of the first byte of the Information (Payload)
portion, as presented in Table 92 .
STEP 4 - Specifying which byte-field (within the
E3 frame) that the LAPD Message frame octets
are to be transported on.
The Transmit E3 Framer block allows the user to
transport the LAPD Message frame octets via either
the “NR” byte or the “GC” byte-field, within each Out-
bound E3 frame. The user makes this selection by
writing the appropriate value to bit-field 4 (DLinNR),
within the Tx E3 Configuration Register, as depicted
below.
)
TXE3 CONFIGURATION REGISTER (ADDRESS = 0X30)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Not Used
TxDL
in NR
Not Used
TxAIS
Enable
TxLOS
Enable
TxMARx
RO
RO
RO
R/W
RO
R/W
R/W
R/W
0
0
0
0
0
0
0
0
If the user writes a “0” into this bit-field, then the
LAPD Transmitter will transmit the comprising octets
of the Outbound LAPD Message frame via the GC
byte field. Additionally, the Transmit E3 Framer block
will insert the contents of the TxNR Byte Register
(Address = 0x37) into the “NR” byte of each Out-
bound E3 frame.
Conversely, if the user writes a “1” into this bit-field,
then the LAPD Transmitter will transmit the Outbound
LAPD Message frame octets via the NR byte-field,
within each Outbound E3 frame. Additionally, the
Transmit E3 Framer will insert the contents of the Tx
GC Byte Register (Address = 0x35) into the GC byte-
field of each Outbound E3 frame.
STEP 5 - Specify whether the LAPD Transmitter
should transmit the LAPD Message frame only
once, or an indefinite number of times at One-
Second intervals.
The Transmit E3 HDLC Control block allows the user
to configure the LAPD Transmitter to transmit this
LAPD Message frame only once, or an indefinite
number of times at One-Second intervals. The user
implements this configuration by writing the appropri-
ate value into Bit 3 (Auto Retransmit) within the Tx E3
LAPD Configuration Register (Address = 0x33), as
depicted below.
)
TXE3 LAPD CONFIGURATION REGISTER (ADDRESS = 0X33)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Not Used
Auto
Retransmit
Not Used
TxLAPD
Msg Length
TxLAPD
Enable
RO
RO
RO
RO
R/W
RO
R/W
R/W
0
0
0
0
1
0
0
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
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