XRT7250 Datasheet, PDF (213/463 Pages) Exar Corporation – DS3/E3 FRAMER IC

XRT7250 DS3/E3 FRAMER IC
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REV. 1.1.1
if the number of AIS-type M-frames is detected, such
that it meets the following conditions:
NAIS - NVALID > 63
where:
NAIS = the number of M-frames containing the AIS
pattern.
If at anytime, the contents of this Up/Down counter
exceeds 63 M-frames, then the Receive DS3 Framer
block will:
1. Assert the RxAIS output pin by toggling it "High".
2. Set Bit 7 (RxAIS) within the Rx DS3 Configuration
and Status Register, to "1" as depicted below.
NVALID = the number of M-frames not containing the
AIS pattern
RX DS3 CONFIGURATION AND STATUS REGISTER, (ADDRESS = 0X10)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT2
BIT 1
BIT 0
RxAIS
1
RxLOS
X
RxIdle
X
RxOOF
X
Int LOS
Disable
X
Framing on
Parity
X
F-Sync Algo M-Sync Algo
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 con-
dition 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 Receive 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 condi-
tions.
• 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.
The Receive DS3 Framer block circuitry includes an
Up/Down Counter that is used to track the number of
M-frames that have been identified as exhibiting the
Idle Condition by the Receive DS3 Framer block. The
contents of this counter are set to zero upon reset or
power up. This counter is then incremented whenev-
er the Receive DS3 Framer block detects an Idle-type
M-frame. The counter is decremented, or kept at ze-
ro if a non-Idle M-frame is detected. If the Receive
DS3 Framer block detects a sufficient number of Idle-
type M-frames, such that the counter reaches the
number 63, then the Receive DS3 Framer block will
declare the Idle Condition. Explained another way,
the Receive DS3 Framer block will declare an Idle
Condition if the number of Idle-Pattern M-frames is
detected such that it meets the following conditions.
NIDLE - NVALID > 63,
where:
NIDLE = the number of M-frames containing the Idle
Pattern
NVALID = the number of M-frames not exhibit the Idle
Pattern
Anytime the contents of this Up/Down Counter reach-
es the number 63, then the Receive DS3 Framer
block will:
1. Set Bit 5 (RxIdle) within the Rx DS3 Configuration
and Status Register, to "1" as depicted below.
RX DS3 CONFIGURATION AND STATUS REGIS-
TER, (ADDRESS = 0X10)
RX DS3 CONFIGURATION AND STATUS REGISTER, (ADDRESS = 0X10)
BIT 7
RxAIS
R/O
X
BIT 6
RxLOS
R/O
X
BIT 5
RxIdle
R/O
1
BIT 4
RxOOF
R/O
X
BIT 3
Int LOS
Disable
R/W
X
BIT2
Framing on
Parity
R/W
X
BIT 1
BIT 0
F-Sync Algo M-Sync Algo
R/W
R/W
X
X
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