XRT74L73 Datasheet, PDF (241/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

PRELIMINARY
XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
RX DS3 CONFIGURATION AND STATUS REGISTER, (ADDRESS = 0X10)
BIT 7
RO
BIT 6
RO
BIT 5
RO
BIT 4
RO
BIT 3
R/W
BIT2
R/W
BIT 1
R/W
BIT 0
R/W
X
X
X
X
X
X
X
X
Table 54 relates the contents of this bit-field to the
OOF Declaration criteria
TABLE 54: THE RELATIONSHIP BETWEEN THE CONTENTS OF BIT 1 (F-SYNC ALGO) WITHIN THE RX DS3
CONFIGURATION AND STATUS REGISTER, AND THE RESULTING F-BIT OOF DECLARATION CRITERIA USED BY THE
RECEIVE DS3 FRAMER BLOCK
F-SYNC ALGO (BIT 1)
0
1
OOF DECLARATION CRITERIA
OOF is declared when 6 out of 16 consecutive F-bits are in error.
OOF is declared when 3 out of 16 consecutive F-bits are in error.
NOTE: Once the Receive DS3 Framer block has declared
an OOF condition, it will transition back to the F-Bit Search
state within the DS3 Frame Acquisition/Maintenance algo-
rithm (per Figure 88 ).
In addition to selecting an OOF Declaration criteria
for the F-bits, the following options exist for configur-
ing the OOF Declaration criteria based upon M-bits.
1. M-bit errors do not cause a OOF Declaration, or
2. OOF will be declared if 3 out of 4 consecutive M-
bits are in error.
The selection between these two options is made by
writing the appropriate value to Bit 0 (M-Sync Algo)
within the Receive DS3 Configuration and Status
Register, as depicted below.
RX DS3 CONFIGURATION AND STATUS REGISTER, (ADDRESS = 0X10)
BIT 7
RxAIS
BIT 6
RxLOS
BIT 5
RxIdle
BIT 4
RxOOF
BIT 3
Int LOS
Disable
BIT2
Framing on
Parity
BIT 1
BIT 0
F-Sync Algo M-Sync Algo
RO
RO
RO
RO
R/W
R/W
R/W
R/W
X
X
X
X
X
X
X
X
Table 55 relates the contents of this Bit Field to the
M-Bit Error criteria for Declaration of OOF.
TABLE 55: THE RELATIONSHIP BETWEEN THE CONTENTS OF BIT 0 (M-SYNC ALGO) WITHIN THE RX DS3
CONFIGURATION AND STATUS REGISTER, AND THE RESULTING M-BIT OOF DECLARATION CRITERIA USED BY THE
RECEIVE DS3 FRAMER BLOCK
MSYNC ALGO (BIT 0)
0
1
OOF DECLARATION CRITERIA
M-Bit Errors do not result in the declaration of OOF
OOF is declared when 3 out of 4 M-bits are in error.
The Framing on Parity Criteria for OOF Declara-
tion
Finally, the Framer IC offers the Framing on Parity
option, which also effects the OOF Declaration crite-
ria. As was mentioned earlier, the Framer IC allows
the user to configure the Receive DS3 Framer block
to detect ’valid-parity’ before declaring itself In-Frame.
This same selection also configures the Receive DS3
Framer block to also declare an OOF Condition if a P-
bit error is detected in 2 of the last 5 M-frames.
Whenever the Receive DS3 Framer block declares
OOF after being in the In-Frame State the following
will happen.
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