XRT72L56 Datasheet, PDF (272/486 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
áç
PRELIMINARY
condition), then it will inform the Remote Terminal
Equipment of this fact by commanding the Local
Transmit E3 Framer block to set the “A” bit-field, with-
in the next outbound E3 frame, to “1”. The Local
Transmit E3 Framer block will continue to set the “A”
bit-field (within the subsequent outbound E3 frames)
to “1” until the Receive E3 Framer block no longer ex-
periences problems in receiving the E3 frame data. If
the Remote Terminal Equipment receives a certain
number of consecutive E3 frames, with the “A” bit-
field set to “1”, then the Remote Terminal Equipment
will interpret this signaling as an indication of a Far-
End Receive Failure (e.g., a problem with the Local
Terminal Equipment).
Conversely, if the Receive E3 Framer block (at a Lo-
cal Terminal Equipment) is not experiencing any
problems receiving E3 frame data from a Remote Ter-
minal Equipment, then it will also inform the Remote
Terminal Equipment of this fact by commanding the
Local Transmit E3 Framer block to set the “A” bit-field
within an outbound E3 frame (which is destined for
the Remote Terminal) to “0”. The Remote Terminal
Equipment will interpret this form of signaling as an
indication of a normal operation.
A detailed discussion into the practical use of the A
bit-field is presented in Section 4.2.2.
5.1.1.2 The “N” Bit
The “N” bit is typically used to transport PMDL (Path
Maintenance Data Link) information, from one termi-
nal to the next. However, the “N” bit-field can also be
used to transport a proprietary data link, if configured
according.
A detailed discussion into the practical use of the N-
bit field is presented in Section 4.2.2.
5.2 THE TRANSMIT SECTION OF THE XRT72L56 (E3,
ITU-T G.751 MODE OPERATION)
When the XRT72L56 has been configured to operate
in the E3, ITU-T G.751 Mode, the Transmit Section of
the XRT72L56 consists of the following functional
blocks.
• Transmit Payload Data Input Interface block
• Transmit Overhead Data Input Interface block
• Transmit E3 Framer block
• Transmit HDLC Controller block
• Transmit LIU Interface block
Figure 98 presents a simple illustration of the Trans-
mit Section of the XRT72L56 Framer IC.
FIGURE 98. A SIMPLE ILLUSTRATION OF THE XRT72L56 TRANSMIT SECTION WHEN IT HAS BEEN CONFIGURED TO
OPERATE IN THE E3 MODE
TxOHFrame
TxOHEnable
TxOH
TxOHClk
TxOHIns
TxOHInd
TxSer
TxNib[3:0]
TxInClk
TxNibClk
TxFrame
Transmit Overhead
Input
Interface Block
Transmit
Payload Data
Input
Interface Block
Transmit DS3/E3
Framer Block
Transmit LIU
Interface
Block
TxPOS
TxNEG
TxLineClk
From Microprocessor
Interface Block
TTxxEE33HHDDLLCC
CCoonntrtorolllelre/rB/Buufffefrer
Each of these functional blocks will be discussed in
detail in this document.
5.2.1 The Transmit Payload Data Input Interface
Block
Figure 99 presents a simple illustration of the Trans-
mit Payload Data Input Interface block.
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