XRT74L73 Datasheet, PDF (115/488 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
PLCP frame. BIP-8 is an eight bit code in which the
nth bit of the BIP-8 code reflects the even-parity bit
calculated with the nth bit of each octet involved in the
calculation. Thus, the BIP-8 value presents the results
for 8 separate even-bit parity calculations.
• G1—PLCP Path Status
This byte-field contains some diagnostic information
which was compiled by the “Near-End” Receive
PLCP Processor of this UNI device (See Section
TABLE 15: BIT FORMAT OF G1 OCTET
BIT 7
BIT 6
BIT 5
Far End Block Error (FEBE)
4 Bits
BIT 4
7.2.2.2.2). The purpose of this diagnostic byte field is
to inform the Far-End Terminal of whether or not the
(Near End) Receive PLCP Processor of this UNI has
detected errors or has had problems framing to its (the
Far-End Transmit PLCP Processor’s) transmission.
Table 15 presents the bit-format of the G1 octet
which consists of a 4 bit Far-End Block Error (FEBE)
subfield, a 1 bit RAI (Yellow) alarm and 3 X-bits (the X
bits are ignored).
BIT 3
RAI (Yellow)
1 Bit
BIT 2
BIT 1
BIT 0
X bits (Ignored by the Receiver)
3 Bits
• C1—Stuffing Status/Nibble-Trailer Length
Indicator Byte
Table 13 indicates that the PLCP frame will contain a nib-
ble trailer of either 13 or 14 nibbles, appended to the end of
each PLCP frame. This option of using either 13 or 14 nib-
bles presents the Transmit PLCP processor with a stuff
opportunity. This octet (C1) conveys the nibble stuffing
status and is also the nibble length indicator for the current
PLCP frame. For more information on the C1 octet, please
see Section 6.3.3.1.
2.3.3Functional Description of the Transmit PLCP
Processor Block
Figure 19 presents a functional block diagram of the
Transmit PLCP Processor.
FIGURE 19. FUNCTIONAL BLOCK DIAGRAM OF THE TRANSMIT PLCP PROCESSOR
To/From
Tx Cell
Processor
StuffCtl
8kRef
TimeRefSel
RxPStuff
From ^RxFEBE
Rx PLCP _{RxYellowAlarm}
RxPFrame
To/From
Pins
TxPOH
TxPOHClk
TxPOHFrame
TxPOHIns
Controlled
Stuff Generator
C1 Byte
BIP-8
Generator
G1 Byte
Generator
Framing Bytes,
POI, Dummy
POH Generator
External POH
Collector
TxNibbleData
Over Head
MUX
Over Head
Payload
MUX
Byte/Nibble
Converter
From/To
DS3
Framer
Block
TxNibbleClock
OH
Address
PayLoad/OH
TxPFrame
Row
Counter
(12)
Stuff
Counter
(13/14)
Column
Counter
(57)
Byte
Clock
Generator
Byte Clock
Nibble Clock
Timing & Control
Figure 19 indicates that the Transmit PLCP Processor • Controlled Stuff Generator, C1 Byte
consists of the following functional blocks.
• BIP-8 Generator
116