XRT7250 datasheet(284/463 Pages) EXAR

284 / 463 page

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XRT7250

DS3/E3 FRAMER IC

REV. 1.1.1

265

The relationship between the contents of bit-fields 1

and the LAPD Message size is given in Table 53.

NOTE: The Message Type selected must correspond with

the contents of the first byte of the Information (Payload)

portion, as presented in Table 52.

STEP 5 - Specify whether the LAPD Transmitter

should transmit the LAPD Message frame only

once, or an indefinite number of times at one-sec-

ond intervals.

The Transmit E3 HDLC Control block allows the user

to configure the LAPD Transmitter to transmit this

LAPD Message frame only once, or an indefinite

number of times at one-second intervals. The user

implements this configuration by writing the appropri-

ate value into Bit 3 (Auto Retransmit) within the Tx E3

LAPD Configuration Register (Address = 0x33), as

depicted below.

)

If the user writes a “1” into this bit-field, then the

LAPD Transmitter will transmit the LAPD Message

frame repeatedly at one-second intervals until the

LAPD Transmitter is disabled.

If the user writes a “0” into this bit-field, then the

LAPD Transmitter will transmit the LAPD Message

frame only once. Afterwards, the LAPD Transmitter

will halt its transmission until the user invokes the

Transmit LAPD Message frame command, once

again.

STEP 5 - Enabling the LAPD Transmitter

Prior to the transmission of any data via the LAPD

Transmitter, the LAPD Transmitter must be enabled.

This is accomplished by writing a "1" to bit 0 (TxLAPD

Enable) of the Tx E3 LAPD Configuration Register, as

depicted below.

If the user writes a “0” into this bit-field, then the

LAPD Transmitter will be enabled, and the LAPD

Transmitter will immediately begin to transmit a con-

tinuous stream of Flag Sequence octets (0x7E), via

the “N” bit-field of each outbound E3 frame.

Conversely, if the user writes a “1” into this bit-field,

then the LAPD Transmitter will be disabled. The

Transmit E3 Framer block will automatically insert a

“1” into the “N” bit-field, within each outbound E3

frame. No transmission of PMDL data will occur.

STEP 7 - Initiate the Transmission

At this point, the user should have written the PMDL

message into the on-chip Transmit LAPD Message

buffer and the type of LAPD Message that is desired

to be transmitted should have been specified. Finally,

TABLE 53: RELATIONSHIP BETWEEN TXLAPD MSG LENGTH AND THE LAPD MESSAGE SIZE

TXLAPD MESSAGE LENGTH

LAPD MESSAGE LENGTH

LAPD Message size is 76 bytes

LAPD Message size is 82 bytes

TXE3 LAPD CONFIGURATION REGISTER (ADDRESS = 0X33)

BIT 7BIT 6BIT 5BIT 4BIT 3BIT 2BIT 1BIT 0

Not Used

Auto

Retransmit

Not Used

TxLAPD

Msg Length

TxLAPD

Enable

R/W

0001

000

TRANSMIT E3 LAPD CONFIGURATION REGISTER (ADDRESS = 0X33)

BIT 7BIT 6BIT 5BIT 4BIT 3BIT2BIT 1

BIT 0

Not Used

Auto

Retransmit

Not Used

TxLAPD

Msg Length

TxLAPD

Enable

R/O

E/O

R/W

R/O

R/W

000

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