XRT72L56 Datasheet, PDF (167/486 Pages) Exar Corporation – SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
PRELIMINARY
FRAMER OPERATING MODE REGISTER (ADDRESS = 0X00)
XRT72L56
REV. P1.1.2
BIT 7
BIT 6
BIT 5
BIT 4
x
1
x
0
Table 17 lists the relationship between the value of
the this bit-field and the resulting DS3 Frame Format.
TABLE 17: 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
0
1
DS3 FRAME FORMAT
C-Bit Parity
M13
NOTE: This bit setting also configures the frame format for
both the Transmit and Receive Section of the XRT72L56.
Each of the two DS3 Frame Formats, as presented in
Figure 40 and Figure 41, 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 40 and 41, each F-frame is represented by
BIT 3
BIT2
BIT 1
BIT 0
x
x
x
x
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.
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 shown in
Figure 41), is interpreted as being a stuff bit. In the
C-bit Parity framing format, the C bits take on different
roles, as presented in Table 18.
TABLE 18: 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 _{(UDL) User Data Link (undefined for DS3 Frame)}
C31,C32, C33 _{CP (Path) Parity Bits}
C41, C42, C43 _{FEBE (Far End Block Error) Indicators}
C51, C52, C53 _{(DL) Path Maintenance Data Link}
C61, C62, C63, _{(UDL) User Data Link (undefined for DS3 Frame)}
C71, C72, C73
Definition of the DS3 Frame Overhead Bits
In general, the DS3 Frame Overhead Bits serve the
following three purposes:
1. Support Frame Synchronization between the
Local and Remote DS3 Terminals
2. Provide parity bits in order to facilitate perfor-
mance monitoring and error detection.
3. Support the transmission of Alarms, Status, and
Data Link information to the Remote DS3 Termi-
nal.
The Overhead bits supporting each of these purpos-
es are further defined below.
4.1.1 Frame Synchronization Bits (Applies to
both M13 and C-bit Parity Framing Formats)
Each DS3 Frame (M-frame) contains a total of 31 bits
that support frame synchronization. Each DS3 M-
frame contains three M-bits. According to Figure 40
and Figure 41, these M-bits are the first bits in F-
frames 5, 6 and 7. These three bits appear in each
M-frame with the repeating pattern of "010". This fact
is also presented in Figure 40 and Figure 41, which
contains bit-fields that are designated as: M0, M1,
and M0 (where M0 = "0", and M1 = "1").
Each F-frame contains four F-bits, which also aid in
synchronization between the Local and the remote
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