XRT74L73 Datasheet, PDF (317/488 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
STEP 4 - Specifying the Length of the LAPD Mes-
sage
One of two different sizes of LAPD Messages can be
transmitted. This can be accomplished by writing the
appropriate data to bit 1 within the Tx E3 LAPD Con-
figuration Register. The bit-format of this register is
presented below.
TRANSMIT E3 LAPD CONFIGURATION REGISTER (ADDRESS = 0X33)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT2
BIT 1
BIT 0
Not Used
Auto
Retransmit
Not Used
TxLAPD
Msg Length
TxLAPD
Enable
R/O
R/O
R/O
R/O
R/W
R/O
R/W
R/W
0
0
0
0
X
0
X
X
The relationship between the contents of bit-fields 1
and the LAPD Message size is given in Table 69 .
TABLE 69: RELATIONSHIP BETWEEN TXLAPD MSG LENGTH AND THE LAPD MESSAGE SIZE
TXLAPD MESSAGE LENGTH
0
1
LAPD MESSAGE LENGTH
LAPD Message size is 76 bytes
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 68 .
STEP 5 - Specify whether the LAPD Transmitter
should transmit the LAPD Message frame only
once, or an indefinite number of times at one-sec-
ond 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
Transmit LAPD Message frame command, once
again.
STEP 5 - Enabling the LAPD Transmitter
Prior to the transmission of any data via the LAPD
Transmitter, the LAPD Transmitter must be enabled.
This is accomplished by writing a "1" to bit 0 (TxLAPD
Enable) of the Tx E3 LAPD Configuration Register, as
depicted below.
318