XRT72L13 Datasheet, PDF (282/370 Pages) Exar Corporation – M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC

XRT72L13
M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC
REV. P1.0.6
áç
PRELIMINARY
OPERATING MODE REGISTER (ADDRESS = 0X00)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT2
BIT 1
BIT 0
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
0
1
1
0
1
X
X
X
This action will prevent the LAPD Transmitter from
generating its own "one-second" interrupts.
This can be done by writing a "1" into Bit 0 of the
Block Interrupt Enable Register, as depicted below.
2. Enable the "One-Second" Interrupt
BLOCK INTERRUPT ENABLE REGISTER (ADDRESS = 0X04)
BIT 7
BIT 6
BIT 5
BIT 4
RxDS3/E3
Interrupt
Enable
Not Used
M13
Interrupt
Status
R/W
RO
RO
RO
0
0
0
0
3. Write the new message into the "Transmit LAPD
Message" buffer immediately after the occur-
rence of the "One-Second" interrupt.
By timing the writes to the "Transmit LAPD Message"
buffer to occur immediately after the occurrence of
the "One-Second" interrupt, the user avoids conflict-
ing with the "one-second" transmissions of the LAPD
Message, and will transmit the correct messages to
the "remote" LAPD Receiver.
4.2.4 The Transmit DS3 Framer Block
4.2.4.1 Brief Description of the Transmit DS3
Framer
The Transmit DS3 Framer block accepts data from
any of the following three sources, and uses it to form
the DS3 data stream.
• The Transmit Payload Data Input block
• The Transmit Overhead Data Input block
• The Transmit HDLC Controller block
• The Internal Overhead Data Generator
The manner in how the Transmit DS3 Framer block
handles data from each of these sources is described
below.
Handling of data from the "Transmit Payload Data
Input Interface
For DS3 applications, all data that is input to the
"Transmit Payload Data Input" Interface will be insert-
ed into the payload bit positions within the "outbound"
DS3 frames.
Handling of data from the "Internal Overhead Bit"
Generator
BIT 3
BIT2
BIT 1
BIT 0
Not Used
TxDS3/E3
Interrupt
Enable
One Second
Interrupt
Enable
RO
RO
R/W
R/W
0
0
0
X
By default, the Transmit DS3 Framer block will inter-
nally generate the overhead bits. However, if the Ter-
minal Equipment inserts its own values for the over-
head bits (via the "Transmit Overhead Data Input In-
terface); or if the user enables and employs the
"Transmit DS3 HDLC Controller" block, then these
"internally generated" overhead bits will be overwrit-
ten.
Handling of data from the "Transmit Overhead Da-
ta Input Interface
For DS3 applications, the Transmit DS3 Framer block
automatically generates and inserts the framing align-
ment bits (e.g., the "F" and "M" bits) into the "out-
bound" DS3 frames. Further, the Transmit DS3 Fram-
er block will automatically compute and insert the P-
bits into the "outbound" DS3 frames. Hence, the
Transmit DS3 Framer block will not accept data from
the "Transmit OH Data Input Interface" block for the
"F", "M" and "P" bits.
However, the Transmit DS3 Framer block will accept
(and insert) data from the "Transmit Overhead Data
Input" Interface for the following bit-fields.
• X-bits
• FEBE bits
• FEAC bits
• DL bits
• UDL bits
• CP bits
If the user's local "Data Link" Equipment activates the
"Transmit Overhead Data Input Interface" block and
writes data into this interface for these bits, then the
270