XRT7250 datasheet(354/463 Pages) EXAR

354 / 463 page

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XRT7250

DS3/E3 FRAMER IC

REV. 1.1.1

335

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”.

6.1.1.5

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 contents

of the NR byte-field within each incoming E3 frame

and will write it into the RxNR Byte register. Conse-

quently, 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).

6.1.1.6

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 contents

of the GC byte-field, within each incoming E3 frame,

and will write it into the RxGC Byte register. Conse-

quently, 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).

6.2

THE TRANSMIT SECTION OF THE XRT7250 (E3

MODE OPERATION)

When the XRT7250 has been configured to operate

in the E3, ITU-T G.832 Mode, the Transmit Section of

the XRT7250 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 155 presents a simple illustration of the Trans-

mit Section of the XRT7250 Framer IC.

TABLE 69: A LISTING OF THE VARIOUS PAYLOAD TYPE VALUES AND THEIR CORRESPONDING MEANING

PAYLOAD TYPE

VALUE

MEANING

000

Unequipped

001

Equipped

010

ATM Cells

011

SDH TU-12s

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