XRT72L50 Datasheet, PDF (284/471 Pages) Exar Corporation – SINGLE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
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ultimately be used by the Remote Terminal Equipment in order to help it identify the type of LAPD message
frame that it is receiving. Table 49 lists these octets and the corresponding LAPD Message types.
STEP 3 - Write the PMDL Message into the remaining part of the Transmit LAPD Message Buffer.
The user must now write in the PMDL Message into the remaining portion of the Transmit LAPD Message
buffer (e.g., addresses 0x8B through 0xDB).
STEP 4 - Specifying the Length of the LAPD Message
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 Configuration Register. The bit-format of this register is
presented 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
X
The relationship between the contents of bit-fields 1 and the LAPD Message size is given in Table 50.
TABLE 50: 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 49.
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 appropriate 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
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 5 - Enabling the LAPD Transmitter
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