XRT72L13 Datasheet, PDF (239/370 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
4.0 CLEAR CHANNEL FRAMER OPERATION OF Section 5.0 - High-Speed HDLC Controller (e.g.,
THE XRT72L13
Frame-Relay over DS3) Mode.
The XRT72L13 M13/Framer IC can be configured to
operate in any of the following modes:
• Clear-Channel Framer Mode
• Channelized (M13) Mode
• High-Speed HDLC Controller Mode.
Section 6.0 - Diagnostic Features of the XRT72L13.
This section will discuss Clear-Channel Framer Mode
operation of the XRT72L13, in detail.
Configuring the XRT72L13 to Operate in the
Clear-Channel Framer Mode
As a consequence, the discussion of the XRT72L13
will be organized as follows:
Section 4.0 - Clear Channel Framer Mode Operation
of the XRT72L13.
Section 5.0 - Channelized (M13) Mode Operation of
the XRT72L13.
The XRT72L13 can be configured to operate in the
"Clear-Channel Framer" Mode by writing a "0" into bit-
field 6 (Payload HDLC Controller Enable) and bit 4
(M13 Disable) within the “M23 Configuration" register;
as illustrated below.
M23 CONFIGURATION REGISTER (ADDRESS = 0X07)
BIT 7
Unused
R/O
x
BIT 6
Payload
HDLC
Controller
Enable
R/W
0
BIT 5
RxDS1Clk
Gapped
(CRC-32)
R/W
x
BIT 4
M13
Disable
R/W
1
The XRT72L13 can be configured to support either
the “DS3 M13” or the “DS3 C-Bit Parity” framing for-
mats. Prior to describing the functional blocks within
the Transmit and Receive Sections of the XRT72L13;
it is important to describe these following two framing
formats.
• M13
• C-Bit Parity
4.1 DESCRIPTION OF THE DS3 FRAMES AND ASSOCI-
ATED OVERHEAD BITS
BIT 3
BIT2
BIT 1
BIT 0
M13
Loop-back
(Remote
Loop-back)
Tributary
Polarity
M23 Loop-back
Code[1:0]
R/W
R/W
R/W
R/W
x
x
x
x
The role of the various overhead bits are best de-
scribed by discussing the DS3 Frame Format as a
whole. The DS3 Frame contains 4760 bits, of which
56 bits are overhead and the remaining 4704 bits are
"payload" bits. The "payload" data is formatted into
packets of 84 bits and the overhead (OH) bits are in-
serted between these payload packets. The
XRT72L13 Framer device supports the following two
DS3 framing formats:
• C-bit Parity
• M13
Figures 59 and 60 present the DS3 Frame Format
for C-bit Parity and M13, respectively.
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