XRT72L13 Datasheet, PDF (241/370 Pages) Exar Corporation – M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC

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PRELIMINARY
XRT72L13
M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC
REV. P1.0.6
OPERATING MODE REGISTER (ADDRESS = 0X00)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT2
BIT 1
BIT 0
Local Loop- Line Loop- Internal LOS
back Mode back Mode
Enable
RESET
R/W
R/W
R/W
R/W
x
1
x
0
Table 10 lists the relationship between the value of
the this bit-field and the resulting DS3 Frame Format.
TABLE 10: THE RELATIONSHIP BETWEEN THE CONTENT
OF BIT 2, (C-BIT PARITY*/M13) WITHIN THE "FRAMER
OPERATING MODE" REGISTER AND THE RESULTING
DS3 FRAMING FORMAT
BIT 2
DS3 FRAME FORMAT
0
C-Bit Parity
1
M13
NOTE: This bit setting also configures the frame format for
both the Transmit and Receive Section of the XRT72L13.
Each of the two DS3 Frame Formats, as presented in
Figure 59 and Figure 60 , 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
Figure 59 and 60 , each F-frame is represented by
the individual rows of payload and overhead bits.
Each F-frame can be further divided into 8 blocks of
85 bits, with 84 of the 85 bits available for payload in-
formation and the remaining one bit used for frame
overhead.
Interrupt
Enable
Reset
Frame Format
TimRefSel[1:0]
R/W
R/W
R/W
R/W
x
x
x
x
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.
M13 Framing Format
In the M13 Format, the C-bits typically reflect the sta-
tus of stuff-opportunities 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
shown in Figure 60 ), is interpreted as being a stuff
bit.
NOTES:
1. For “Clear-Channel Framing” applications, each of
these 21 C-bits will automatically set to “0”.
2. For “Channelized” applications, then these C-bits
will reflect the “stuff-bit” status of the composite
DS2/ITU-T G.747 signals, wiithin the DS3 signal.
C-Bit Parity Framing Format
In the C-bit Parity framing format, the "C" bits take on
different roles, as presented in Table 11 .
TABLE 11: C-BIT FUNCTIONS FOR THE C-BIT PARITY DS3 FRAME FORMAT
C - BIT
FUNCTION OF C-BITS WHILE IN THE C-BIT PARITY FRAMING FORMAT
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, User Data Link (undefined for DS3 Frame)
C71, C72, C73
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