á
PRELIMINARY
DS3 UNI FOR ATM
XRT7245
REV. 1.03
197
Each of these steps will be discussed in detail.
Specifying the Type of LAPD Message
The user can transmit one of four different types of
LAPD Messages. He/she can accomplish this by
writing the appropriate data to bits 1 and 2 of the Tx
DS3 LAPD Configuration Register. The bit-format of
this register is presented below.
The relationship between the contents of bit-fields 1
and 2 and the LAPD Message type follows.
Note:
The Message Type selected must correspond with
the contents of the first byte of the Information (Payload)
portion, as presented in Table 33.
Enabling the LAPD Transmitter
Prior to the transmission of any data via the LAPD
Transmitter, the user must enable the LAPD
Transmitter. He/she can accomplish this by writing a
“1” to bit 0 of the Tx DS3 LAPD Configuration Register,
as depicted below.
Bit 0—TxLAPD Enable
This bit-field allows the user to enable or disable the
LAPD Transmitter in accordance with the following ta-
ble.
Transmit DS3 LAPD Configuration Register (Address = 1Eh)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Unused
Auto Retransmit
TxLAPD Type[1]
TxLAPD Type[0]
TxLAPD Enable
R/W
R/W
R/W
R/W
T
ABLE
33: R
ELATIONSHIP
BETWEEN
T
X
LAPDT
YPE
[1:0]
AND
THE
LAPD M
ESSAGE
T
YPE
/S
IZE
T
X
LAPD T
YPE
[1, 0]
LAPD M
ESSAGE
T
YPE
/S
IZE
00
LAPD Message type is “Test Signal” type. The size of this message is 76 bytes
01
LAPD Message type is “Idle Signal Identification” type. The size of this message is 76 bytes.
10
LAPD Message type is “CL Path Identification Type”. The size of this message is 76 bytes
11
LAPD Message type is “ITU Path Identification Type”. The size of this message is 82 bytes.
Transmit DS3 LAPD Configuration Register (Address = 1Eh)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Unused
Auto Retransmit
TxLAPD Type[1]
TxLAPD Type[0]
TxLAPD Enable
R/W
R/W
R/W
R/W
T
ABLE
34: T
HE
R
ELATIONSHIP
BETWEEN
THE
CONTENT
OF
THE
“T
X
LAPD E
NABLE
”
BIT
-
FIELD
AND
THE
ACTION
OF
THE
LAPD T
RANSMITTER
T
X
LAPD
E
NABLE
R
ESULTING
A
CTION
OF
THE
LAPD T
RANSMITTER
0
The LAPD Transmitter is disabled and the DL bits, in the DS3 frame, are transmitted as all “1”s.
1
The LAPD Transmitter is enabled and is transmitting a continuous stream of Flag Sequence octets (7Eh).