XRT72L56 Datasheet, PDF (410/486 Pages) Exar Corporation – SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

XRT72L56
SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
REV. P1.1.2
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PRELIMINARY
ment. In order to avoid this problem, while writing the
new message into the Transmit LAPD Message buff-
er, the user should do the following.
1. Configure the Framer to automatically reset acti-
vated interrupts.
The user can do this by writing a “1” into Bit 3 within
the Framer Operating Mode register (Address =
0x00), as depicted below.
FRAMER OPERATING MODE REGISTER (ADDRESS = 0X00)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Local Loopback DS3/E3*
Internal
LOS
Enable
RESET
Interrupt
Enable Reset
Frame Format
TimRefSel[1:0]
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
0
0
1
0
1
0
1
1
This action will prevent the LAPD Transmitter from
generating its own One-Second interrupt (following
each transmission of the LAPD Message frame).
2. Enable the One-Second Interrupt
This can be done by writing a “1” into Bit 0 (One-Sec-
ond Interrupt Enable) within the Block Interrupt En-
able Register, as depicted below.
BLOCK INTERRUPT ENABLE REGISTER (ADDRESS = 0X04)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
RxDS3/E3
Interrupt
Enable
Not Used
TxDS3/E3
Interrupt
Enable
One-Second
Interrupt
Enable
R/W
RO
RO
RO
RO
RO
R/W
R/W
0
0
0
0
0
0
0
0
3. Write the new message into the Transmit LAPD
Message buffer immediately after the occurrence
of the One-Second Interrupt
By synchronizing the writes to the Transmit LAPD
Message buffer to occur immediately after the occur-
rence of the One-Second Interrupt, the user avoids
conflicting with the One-Second transmission of the
LAPD Message frame, and will transmit the correct
(uncorrupted) PMDL Message to the Remote LAPD
Receiver.
6.2.4 The Transmit E3 Framer Block
6.2.4.1 Brief Description of the Transmit E3
Framer
The Transmit E3 Framer block accepts data from any
of the following three sources, and uses it to form the
E3 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 E3 Framer block
handles data from each of these sources is described
below.
Handling of data from the Transmit Payload Data
Input Interface
For E3 applications, all data that is input to the Trans-
mit Payload Data Input Interface will be inserted into
the payload bit positions within the Outbound E3
frames.
Handling of data from the Internal Overhead Bit
Generator
By default, the Transmit E3 Framer block will internal-
ly generate the overhead bytes. However, if the Ter-
minal Equipment inserts its own values for the over-
head bits or bytes (via the Transmit Overhead Data
Input Interface) or, if the user enables and employs
the Transmit E3 HDLC Controller block, then these in-
ternally generated overhead bytes will be overwritten.
Handling of data from the Transmit Overhead Da-
ta Input Interface
391