XRT72L50
á
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
271
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.
The relationship between the contents of bit-fields 1 and the LAPD Message size is given in
Table 50.NOTE: The Message Type selected must correspond with the contents of the first byte of the Information (Payload) portion,
as presented in
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.
)
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
Transmit E3 LAPD Configuration Register (Address = 0x33)
BIT 7BIT 6BIT 5BIT 4BIT 3BIT2
BIT 1BIT 0
Not Used
Auto
Retransmit
Not Used
TxLAPD
Msg Length
TxLAPD
Enable
RO
R/W
RO
R/W
00
X
0
XX
TABLE 50: 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
TxE3 LAPD Configuration Register (Address = 0x33)
BIT 7BIT 6BIT 5BIT 4
BIT 3BIT 2BIT 1BIT 0
Not Used
Auto
Retransmit
Not Used
TxLAPD
Msg Length
TxLAPD
Enable
RO
R/W
RO
R/W
00
1
000