XRT7250 Datasheet, PDF (188/463 Pages) Exar Corporation – DS3/E3 FRAMER IC

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DS3/E3 FRAMER IC
XRT7250
REV. 1.1.1
4.2.4.2.1 Generating Alarm Conditions
The Transmit DS3 Framer block permits the user to,
by writing the appropriate data into the on-chip regis-
ters, to override the data that is being written into the
Transmit Payload Data and Overhead Data Input In-
terfaces and transmit the following alarm conditions.
• Generate the Yellow Alarms (or FERF indicators)
• Manipulate the X-bit (set them to 1)
• Generate the AIS Pattern
• Generate the IDLE pattern
• Generate the LOS pattern
• Generate FERF (Yellow) Alarms, in response to
detection of a Red Alarm condition (via the Receive
Section of the XRT7250).
• Generate and transmit a desired value for FEBE
(Far-End-Block Error).
The procedure and results of generating any of these
alarm conditions is presented below.
The user can exercise each of these options by writ-
ing the appropriate data to the Tx DS3 Configuration
Register (Address = 0x30). The bit format of this reg-
ister is presented below.
TX DS3 CONFIGURATION REGISTER (ADDRESS = 0X30)
BIT 7
BIT 6
BIT 5
BIT 4
Tx
Yellow Alarm
R/W
0
Tx X-Bit
R/W
0
Tx IDLE
Pattern
R/W
1
Tx AIS
Pattern
R/W
0
The role/function of each of these bit-fields within the
register, are discussed below.
4.2.4.2.1.1 Transmit Yellow Alarm - Bit 7
This read/write bit field permits the user to force the
transmission of a Yellow Alarm to the remote terminal
BIT 3
BIT2
BIT 1
BIT 0
Tx LOS
Pattern
R/W
1
FERF on
LOS
R/W
0
FERF on
OOF
R/W
1
FERF on
AIS
R/W
1
equipment via software control. If the user opts to
transmit a Yellow Alarm then both of the X-bits, within
the outbound DS3 frames will be set to '0'. Table 27
relates the content of this bit field to the Transmit DS3
Framer block's action.
TABLE 27: THE RELATIONSHIP BETWEEN THE CONTENTS OF BIT 7 (TX YELLOW ALARM) WITHIN THE TX DS3
CONFIGURATION REGISTER, AND THE RESULTING TRANSMIT DS3 FRAMER BLOCK'S ACTION
BIT 7
0
1
TRANSMIT DS3 FRAMER'S ACTION
Normal Operation:
The X-bits are generated by the Transmit DS3 Framer block based upon Near End Receiving Conditions (as
detected by the Receive Section of the chip)
Transmit Yellow Alarm:
The Transmit DS3 Framer block will overwrite the X-bits by setting them all to 0. The payload information is
not modified and is transmitted as normal.
NOTE: This bit is ignored when either the TxIDLE, TxAIS, or
the TxLOS bit-fields are set.
4.2.4.2.1.2 Transmit X-bit - Bit 6
This bit field functions as the logical complement to
Bit 7 (e.g., Tx Yellow Alarm). This read/write bit field
permits the user to force all of the X-bits, in the out-
bound DS3 frames, to "1" and transmit them to the re-
mote terminal equipment. Table 28 relates the con-
tent of this bit field to the Transmit DS3 Framer
Block's action.
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