XRT74L73 Datasheet, PDF (244/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
PRELIMINARY
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 Receive DS3
Framer block will declare an AIS Condition if this
counter reaches the value of 63 M-frames or great-
er. Explained another way, the AIS condition is de-
clared if the number of AIS-type M-frames is detect-
ed, such that it meets the following conditions:
NAIS - NVALID > 63
where:
NAIS = the number of M-frames containing the AIS
pattern.
NVALID = the number of M-frames not 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.
RX DS3 CONFIGURATION AND STATUS REGISTER, (ADDRESS = 0X10)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT2
BIT 1
BIT 0
RxAIS
RxLOS
RxIdle
RxOOF
Int LOS
Disable
Framing on F-Sync Algo M-Sync Algo
Parity
RO
RO
RO
RO
R/W
R/W
R/W
R/W
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 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 nega-
tion 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 re-
set or power up. This counter is then incremented
whenever the Receive DS3 Framer block detects an
Idle-type M-frame. The counter is decremented, or
kept at zero if a non-Idle M-frame is detected. If the
Receive DS3 Framer block detects a sufficient num-
ber of Idle-type M-frames, such that the counter
reaches the number 63, then the Receive DS3 Fram-
er block will declare the Idle Condition. Explained an-
other 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)
245