XRT7250 datasheet(390/463 Pages) EXAR

390 / 463 page

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XRT7250

DS3/E3 FRAMER IC

REV. 1.1.1

371

Figure 176 presents the procedure (in white boxes)

which the user should use in order to transmit a PM-

DL Message via the LAPD Transmitter, when the

LAPD Transmitter is configured to transmit a LAPD

Message frame only once, and then halt transmis-

sion.

FIGURE 175. FLOW CHART DEPICTING HOW TO USE THE LAPD TRANSMITTER (LAPD TRANSMITTER IS CONFIGURED

TO RE

-TRANSMIT THE LAPD MESSAGE FRAME REPEATEDLY AT ONE-SECOND INTERVALS)

Start

Write the “LAPD Message frame identification”

octet into the first octet position within the

“Transmit LAPD Message” buffer (Address = 0x86).

Write the PMDL Message into the remaining

portion of the “Transmit LAPD Message” buffer

(from 0x87 to 0xDD).

Specify the type/size of the LAPD Message frame

to be transmitted.

Write in the appropriate value into bits 5 and 6

within the Tx E3 LAPD Configuration Register

Enable the LAPD Transmitter

Initiate the LAPD Message frame transmission.

Specify whether the “outbound” LAPD Message

frame is to be transported via the GC or the NR

byte-fields, within each “outbound” E3 Frame

LAPD Transmitter will generate a continuous

string of “Flag Sequence” bytes. These bytes will

be transported via either the GC or the NR byte

field (depending upon user’s selection).

LAPD Transmitter will “stuff” the contents of the

PMDL Message (residing within the “Transmit

LAPD Message” buffer).

LAPD Transmitter will read out “stuff” PMDL

Message and encapsulate it into a LAPD Message

frame.

LAPD Transmitter will compute and insert the

FCS value, into the LAPD Message frame.

LAPD Transmitter will fragment LAPD Message

frame into “octets” and begin to insert these octets into

the GC or NR byte-field (depending upon user’s

selection) into each “outbound” E3 frame.

Complete transmission of LAPD Message frame.

Generate “Completion of Transmission of LAPD

Message frame Interrupt.

Wait One Second. Generate a continuous

string of Flag Sequence Bytes

Configure the LAPD Transmitter to repeat transmissions

of the LAPD Message frame at one-second intervals.

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