XRT74L74 Datasheet, PDF (142/498 Pages) Exar Corporation – 4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

XRT74L74
4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.1.1
PRELIMINARY
Figure 24 indicates that the PLCP Frame consists of
12 ATM Cells, 48 bytes of Overhead (OH) bytes, and
13 or 14 nibbles of “trailer” for frequency justification.
TABLE 19: BYTE FORMAT OF THE PLCP FRAME
PLCP FRAME
2 BYTES
A1
A2
A1
A2
A1
A2
A1
A2
A1
A2
A1
A2
A1
A2
A1
A2
A1
A2
A1
A2
A1
A2
A1
A2
POI
1 BYTE
P11
P10
P9
P8
P7
P6
P5
P4
P3
P2
P1
P0
POH
1 BYTE
Z6
Z5
Z4
Z3
Z2
Z1
X
B1
G1
X
X
C1
PLCP PAYLOAD
53 BYTES
First ATM Cell
ATM Cell
ATM Cell
ATM Cell
ATM Cell
ATM Cell
ATM Cell
ATM Cell
ATM Cell
ATM Cell
ATM Cell
Twelfth ATM Cell
13-14 NIBBLES
Trailer
The contents of the Path Overhead (POH) bytes (e.g.,
Z6 through C1) of the incoming PLCP frame is output
via a serial port consisting of the RxPOH, RxPOHClk,
and RxPOHFrame output pins. This serial output port
is discussed in greater detail in section 7.2.2.3.
4.2.2.1 PLCP Framing
At any given time, the Receive PLCP Processor will
be operating in any one of three (3) “framing” modes.
• Un-Framed
• Out-of-Frame (OOF)
• In-Frame
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