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PRELIMINARY
DS3 UNI FOR ATM
XRT7245
REV. 1.03
189
The user can choose between these two frame formats,
by writing the appropriate data to bit 2 of the UNI
Operating Mode Register (Address = 00h), as
depicted below.
The following table lists the relationship between the
value of the this bit-field and the resulting DS3 Frame
Format.
The Transmit DS3 Framer will be operating in the
C-Bit Parity frame format, upon power up or reset.
Therefore, the user must write a “1” to this bit field
in order to configure the Framer to operate in the
M13 Mode.
Note:
This bit setting also configures the frame format for
the Receive DS3 Framer block as well.
Each of the two DS3 Frame Formats, as presented in
Tables 27 and 28 constitute an M-frame (or a full DS3
Frame). Each M-frame consists of 7-680 bit F-frames
(sometimes referred to as, subframes). In Tables 27
and 28, each F-frame is represented by the individual
rows of payload and OH bits. Each F-frame can be
further divided into 8 blocks of 85 bits, with 84 of the
85 bits available for payload information and the
remaining one bit used for frame overhead.
Differences Between the M13 and C-Bit Parity
Frame Formats
The frame formats for M13 and C-bit Parity are very
similar. However, the main difference between these
two framing formats is in the use of the C-bits. In the
M13 Format, the C-bits reflect the status of stuff-op-
portunities that either were or were not used while
multiplexing the 7 DS2 signals into this DS3 signal. If
two of the three stuff bits, within a F-frame, are “1”,
then the associated stuff bit, Si (not shows in Table
28), is interpreted as being a stuff bit. In the C-bit
Parity framing format, the “C” bits take on different
roles, as presented in TTable 30.
UNI Operating Mode Register: Address = 00h
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Local
Loopback
Cell
Loopback
PLCP
Loopback
Reset
Direct
Mapped ATM
M13/C-Bit*
TimRefSel[1, 0]
R/W
R/W
R/W
R/W
R/W
R/W
R/W
T
ABLE
29: T
HE
R
ELATIONSHIP
BETWEEN
THE
CONTENT
OF
B
IT
2, (C-B
IT
P
ARITY
*/M13)
WITHIN
THE
UNI O
PERATING
M
ODE
R
EGISTER
AND
THE
RESULTING
DS3 F
RAMING
F
ORMAT
B
IT
2
DS3 F
RAME
F
ORMAT
0
C-Bit Parity
1
M13
T
ABLE
30: C-
BIT
F
UNCTIONS
FOR
THE
C-
BIT
P
ARITY
DS3 F
RAME
F
ORMAT
C-B
IT
F
UNCTION
OF
C-
BITS
WHILE
IN
THE
C-B
IT
P
ARITY
F
RAMING
F
ORMAT
C11
AIC (C-Bit Parity Mode)
C12
NA (Reserved for Network Application)
C13
FEAC (Far End Alarm & Control)
C21, C22, C23
User Data Link (undefined for DS3 Frame)
C31, C32, C33
C-bit Parity bits
C41, C42, C43
FEBE (Far End Block Error) Indicators
C51, C52, C53
Path Maintenance Data Link
C61, C62, C63, C71, C72, C73
User Data Link (undefined for DS3 Frame)