XRT7250 Datasheet, PDF (254/463 Pages) Exar Corporation – DS3/E3 FRAMER IC

áç
XRT7250
DS3/E3 FRAMER IC
REV. 1.1.1
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 XRT7250 (E3,
ITU-T G.751 MODE OPERATION)
When the XRT7250 has been configured to operate
in the E3, ITU-T G.751 Mode, the Transmit Section of
the XRT7250 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 XRT7250 Framer IC.
FIGURE 98. A SIMPLE ILLUSTRATION OF THE XRT7250 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.
235