XRT7250 datasheet(179/463 Pages) EXAR

179 / 463 page

XRT7250

DS3/E3 FRAMER IC

áç

REV. 1.1.1

160

4.2.3

The Transmit DS3 HDLC Controller

The Transmit DS3 HDLC Controller block can be

used to transport either Bit-Oriented Signaling (BOS)

or Message-Oriented Signaling (MOS) type messag-

es or both types of messages to the remote terminal

equipment. Both BOS and MOS types of HDLC mes-

sage processing are discussed in detail below.

4.2.3.1

Bit-Oriented Signaling (or FEAC Mes-

sage) processing via the Transmit DS3 HDLC

Controller.

The Transmit DS3 HDLC Controller block consists of

two major blocks:

• The Transmit FEAC Processor.

• The LAPD Transmitter.

This section describes how to operate the Transmit

FEAC Processor. If the Transmit DS3 Framer is oper-

ating in the C-bit Parity Framing Format then the

FEAC (Far-End Alarm & Control) bit-field of the DS3

Frame can be used to transmit the FEAC messages

(See Figure 42). The FEAC code word is a 6-bit val-

ue which is encapsulated by 10 framing bits, forming

a 16-bit FEAC message of the form:

where '[d5, d4, d3, d2, d1, d0]' is the FEAC code

word. The rightmost bit (e.g., a 1) of the FEAC Mes-

sage, is transmitted first. Since each DS3 frame con-

tains only 1 FEAC bit, 16 DS3 Frames are required to

transmit the 16 bit FEAC Code Message.

The XRT7250 contains the following two registers

that support FEAC Message Transmission.

• Tx DS3 FEAC Register (Address = 0x32)

• Tx DS3 FEAC Configuration and Status Register

(Address = 0x33)

Operating the Transmit FEAC Processor

In order to transmit a FEAC message to the remote

terminal, the user must execute the following steps.

FIGURE 60. BEHAVIOR OF TRANSMIT OVERHEAD DATA INPUT INTERFACE SIGNALS BETWEEN THE XRT7250 AND

THE

TERMINAL EQUIPMENT (FOR METHOD 2)

TxInClk

TxOHFrame

TxOHEnable

TxOHIns

TxOH

Terminal Equipment

samples “TxOHFrame” and

“TxOHEnable” being “HIGH”

Terminal Equipment

responds by asserting

TxOHIns and placing desired

data on TxOH.

XRT7250 samples TxOH

here.

TxOHEnable Pulse # 8

X bit = 0

0111111

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