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PRELIMINARY
DS3 UNI FOR ATM
XRT7245
REV. 1.03
241
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.
7.2.2.1
At any given time, the Receive PLCP Processor will
be operating in any one of three (3) “framing” modes.
PLCP Framing
Un-Framed
Out-of-Frame (OOF)
In-Frame
The State Machine diagram of the Receive PLCP
Processor framing algorithm is presented in Figure 74,
and each of these framing modes are discussed.
7.2.2.1.1
When the Receive PLCP processor is operating in
the “Un-Framed” mode, it does not have any form of
frame synchronization with the incoming PLCP data.
The Un-Framed Mode
The Receive PLCP Processor will indicate that it is in
the “Un-Framed” Mode to external circuitry by assert-
ing both the RxPOOF and RxPLOF output pins and
the “POOF Status” and “PLOF Status” bits within the
Rx PLCP Configuration/Status Register, as depicted
below.
The Receive PLCP Processor will attempt to acquire
PLCP framing once the Receive DS3 Framer has
reached the “In-Frame” state. Specifically, the
Receive PLCP Processor will attempt to find the
F
IGURE
74. S
TATE
M
ACHINE
D
IAGRAM
OF
THE
R
ECEIVE
PLCP P
ROCESSOR
F
RAMING
A
LGORITHM
Un-Framed
Mode
Out-of-Frame
Mode
In-Frame
Mode
2 Consecutive sets of A1, A2, and POI
bytes are correct, and the recovered POIs
are in the correct sequence.
Errors are detected in two
consecutive framing bytes
(A1, A2) or 2 consecutive
POIs are incorrect.
2 Consecutive sets of A1, A2, and POI
bytes are correct, and the recovered POIs
are in the correct sequence.
The OOF
condition
persists for
more than
1ms.
Rx PLCP Configuration/Status Register (Address = 44h)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Unused
Reframe
POOF Status
PLOF Status
Yellow Status
x
x
x
x
x
1
1
x