XRT72L13 Datasheet, PDF (310/370 Pages) Exar Corporation – M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC

XRT72L13
M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC
REV. P1.0.6
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PRELIMINARY
RX DS3 CONFIGURATION AND STATUS REGISTER, (ADDRESS = 0X10)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT2
BIT 1
BIT 0
Rx AIS
Rx LOS
Rx Idle
Rx OOF
Int LOS
Disable
Framing on
Parity
F-Sync
Algo
M-Sync
Algo
RO
RO
RO
RO
R/W
R/W
R/W
R/W
X
X
X
X
1
X
X
X
NOTE: For more information on the "RLOS" input pin,
please see Section 2.1.
4.3.2.5.2 The Alarm Indication Signal (AIS)
The "Receive DS3 Framer" block will identify and de-
clare an "AIS" condition if it detects all of the following
conditions in the incoming DS3 Data Stream:
ceive DS3 Framer" block will declare an "AIS Condi-
tion" if this counter reaches the value of 63 M-frames
or greater. Explained another way, the AIS condition
is declared if the number of "AIS-type" M-frames is
detected, such that it meets the following conditions:
NAIS - NVALID > 63
• Valid M-bits, F-bits and P-bits
where:
• All C-bits are zeros.
• X-bits are set to "1"
• The Payload portion of the DS3 Frame exhibits a
repeating "1010..." pattern.
NAIS = the number of M-frames containing the AIS
pattern.
NVALID = the number of M-frames not containing the
AIS pattern
The "Receive DS3 Framer" block contains, within its
circuitry, an "Up/Down" Counter that supports the "as-
sertion" and "negation" of the AIS condition. This
counter begins with the value of 0x00 upon power up
or reset. The counter is then incremented anytime
the "Receive DS3 Framer" block detects an "AIS
Type" M-frame. This counter is then decremented, or
kept at "zero" value, when the "Receive DS3 Framer"
block detects a "non-AIS" type M-frame. The "Re-
If at anytime, the contents of this "Up/Down" counter
exceeds 63 M-frames, then the "Receive DS3 Fram-
er" block will:
1. Assert the "RxAIS" output pin by toggling it
"high".
2. Set Bit 7 (Rx AIS) within the "Rx DS3 Configura-
tion and Status" Register, to "1" as depicted
below.
RX DS3 CONFIGURATION AND STATUS REGISTER, (ADDRESS = 0X10)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT2
BIT 1
BIT 0
Rx AIS
Rx LOS
Rx Idle
Rx OOF
Int LOS
Disable
Framing on F-Sync Algo M-Sync Algo
Parity
1
X
X
X
X
X
X
X
3. Generate a "Change in AIS Status" Interrupt
Request to the µP/µC.
4. Force the "Transmit Section" to transmit a "FERF"
indication back to the remote terminal.
The "Receive DS3 Framer" block will clear the "AIS"
condition when the following expression is true.
NAIS - NVALID < 0.
In other words, once the "Receive DS3 Framer" block
has detected a sufficient number of normal (or "Non-
AIS") M-frames, such that this "Up/Down" counter
reaches "zero", then the "Receive DS3 Framer" block
will clear the "AIS Condition" indicators. The "Re-
ceive DS3 Framer" block will inform the µC/µP of this
negation of the "AIS Status" by generating a "Change
in AIS Status" interrupt.
4.3.2.5.3 The Idle (Condition) Alarm
The "Receive DS3 Framer" block will identify and de-
clare an "Idle Condition" if it receives a sufficient num-
ber of "M-Frames" that meets all of the following con-
ditions.
• Valid M-bits, F-bits, and P-bits
• The 3 CP-bits (in F-Frame #3) are zeros.
• The X-bits are set to "1"
• The payload portion of the DS3 Frame exhibits a
repeating "1100..." pattern.
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