XRT72L13 Datasheet, PDF (361/370 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
generates this “G.747” signal, it will create a data
stream that has the “G.747 Framing” structure, as
presented below in Figure 124.
FIGURE 124. ILLUSTRATION OF THE “ITU-T G.747 FRAMING” STRUCTURE
FAS Pattern
Payload Bits (159)
AP *
Payload Bits (165)
C11 C12 C13
Payload Bits (165)
C21 C22 C23
Payload Bits (165)
C31 C32 C33
Payload Bits (165)
Configuring the remaining M12 MUX Blocks
The remaining M12 MUX Blocks (e.g., M12 MUX
Blocks numbers 2 through 7) can be configured to op-
erate in the “G.747” Mode, by setting Bit 4 (M12
G.747) to “1” and Bit 5 (M12 Bypass) to “0”, within
each of their corresponding “M12 DS2 Configuration”
Registers (Address locations 0x1B through 0x20).
5.2.1.1.2.1.1 Description of the “ITU-T G.747”
Frames and the Associated Overhead Bits
In order to fully understand and appreciate the role of
the M12 MUX, it is best to first describe the “ITU-T
G.747” Framing Format.
The “ITU-T G.747 Frame” consists of 840 bits, of
which 24 of these bits are overhead bits, and the re-
maining 816 bits are “payload” bits. The “payload”
data is formatted into a single packet of 159 bits (with-
in subframe # 1); and into packets of 165 bits, within
subframes # 2 through 5. As mentioned earlier, these
ITU-T G.747 data streams are created by the M12
MUX performing bit-wise multiplexing of the three (in-
put) E1 signals. As a consequence, each of these
payload packets consists of a repeating bit-wise mul-
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