XRT74L74 Datasheet, PDF (394/498 Pages) Exar Corporation – 4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

XRT74L74
4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.1.1
PRELIMINARY
TABLE 85: VARIOUS PAYLOAD TYPE VALUES AND THEIR CORRESPONDING MEANING
PAYLOAD TYPE
VALUE
MEANING
000
Unequipped
001
Equipped
010
ATM Cells
011
SDH TU-12s
Bits 2 - 1 Payload Dependent
To be provided later.
Bit 0 - Timing Marker
This bit-field is set to “0” to indicate that the timing
source is traceable to a Primary Reference Clock.
Otherwise, this bit-field is set to “1”.
7.1.1.5 The Network Operator (NR) Byte
The NR byte or the GC byte can be configured to
transport LAP-D Message frame octets from the
LAPD Transmitter to the LAPD Receiver (of the Re-
mote Terminal Equipment) at a data rate of 64kbps (1
byte per E3 frame).
If the user opts not to use the NR byte to transport
these LAPD Message frames, then the Transmit E3
Framer block will read in the contents of the TxNR
Byte Register (Address = 0x37), and insert this value
into the NR byte-field of each Outbound E3 frame.
The Receive E3 Framer block will read in the con-
tents of the NR byte-field within each incoming E3
frame and will write it into the RxNR Byte register.
Consequently, the user can determine the value of
the NR byte, within the most recently received E3
frame by reading the Rx NR Byte Register (Address =
0x1A).
7.1.1.6 The General Purpose Communica-
tions Channel (GC) Byte
The NR byte or the GC byte can be configured to
transport LAPD Message frames from the LAPD
Transmitter to the LAPD Receiver (of the Remote Ter-
minal Equipment) at a data rate of 64kbps (1 byte per
E3 frame).
If the user opts not to use the GC byte to transport
these LAPD Message frames, then the Transmit E3
Framer block will read in the contents of the Tx GC
Byte Register (Address = 0x35), and insert this value
into the GC byte-field of each Outbound E3 frame.
The Receive E3 Framer block will read in the con-
tents of the GC byte-field, within each incoming E3
frame, and will write it into the RxGC Byte register.
Consequently, the user can determine the value of
the GC byte, within the most recently received E3
frame, by reading the Rx GC Byte register (Address =
0x1B).
7.2 THE TRANSMIT SECTION OF THE XRT74L74 (E3
MODE OPERATION)
When the XRT74L74 has been configured to operate
in the E3, ITU-T G.832 Mode, the Transmit Section of
the XRT74L74 consists of the following functional
blocks.
• Transmit Payload Data Input Interface block
• Transmit Overhead Data Input Interface block
• Transmit E3 Framer block
• Transmit HDLC Controller block
• Transmit LIU Interface block
Figure 162 presents a simple illustration of the
Transmit Section of the XRT74L74 Framer IC.
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