XRT72L50 Datasheet, PDF (180/471 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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The Message Type selected must correspond with the contents of the first byte of the Information (Payload)
portion, as presented in Table 21 and written at address 0x8A.
STEP 2 - 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 of the Tx DS3 LAPD Configuration Register, as depicted below.
Transmit DS3 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
Bit 0 - TxLAPD Enable
This bit-field allows the user to enable or disable the LAPD Transmitter in accordance with Table 23.
TABLE 23: RELATIONSHIP BETWEEN TXLAPD MSG LENGTH AND THE LAPD MESSAGE SIZE
TXLAPD ENABLE
0
1
RESULTING ACTION OF THE LAPD TRANSMITTER
The LAPD Transmitter is disabled and the DL bits, in the DS3 frame,
are transmitted as all 1’s.
The LAPD Transmitter is enabled and is transmitting a continuous
stream of Flag Sequence octets (0x7E).
Prior to executing Step 2, the LAPD Transmitter is disabled and the Transmit DS3 Framer block is setting each
of the DL bits within the outbound DS3 data stream to “1”. After this step is executed, the LAPD Transmitter
begins transmitting the flag sequence octet (0x7E) via the DL bits.
NOTE: Upon power up or reset, the LAPD Transmitter is disabled. Therefore, this bit must be set to a "1" in order to enable
the LAPD Transmitter.
STEP 3 - Initiate the Transmission
At this point, the LAPD Transmitter is ready to begin transmission. The user has written the information portion
of the PMDL message into the on-chip Transmit LAPD Message buffer. Further, the user has specified the
type of LAPD message that is to be transmitted and has enabled the LAPD Transmitter. To initiate the
transmission of this message, write a "1" to Bit 3 (TxDL Start) of the Tx DS3 LAPD Status/Interrupt Register.
The bit format of this register is presented below.
Transmit DS3 LAPD Status/Interrupt Register (Address = 0x34)
BIT 7
RO
0
BIT 6
BIT 5
Not Used
RO
RO
0
0
BIT 4
RO
0
BIT 3
Tx DL
Start
R/W
1
BIT2
Tx DL
Busy
RO
X
BIT 1
TxLAPD
Interrupt
Enable
R/W
X
BIT 0
TxLAPD
Interrupt
Status
RUR
X
A "0" to "1" transition of Bit 3 (TxDL Start) in this register, initiates the transmission of the data link message.
While the LAPD transmitter is transmitting the message, Bit 2 (TxDL Busy) is set to “1”. This bit-field allows the
user to poll the status of the LAPD Transmitter. Once the message transfer is completed, this bit-field toggles
back to “0”.
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