XRT7250 datasheet(326/463 Pages) EXAR

326 / 463 page

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XRT7250

DS3/E3 FRAMER IC

REV. 1.1.1

307

Table 62 presents the relationship between the con-

tents of RxLAPDType[1:0] and the type of message

received by the LAPD Receiver.

NOTE: Prior to reading in the PMDL Message from the

Receive LAPD Message buffer, the user is urged to read

the state of the RxLAPDType[1:0] bit-fields in order to deter-

mine the size of this message.

5. Inform the Local Microprocessor/External Cir-

cuitry of the receipt of the new LAPD Message

frame.

Finally, after the LAPD Receiver has received and

processed the newly received LAPD Message frame

(per steps 1 through 4, as described above), it will in-

form the local Microprocessor that a LAPD Message

frame has been received and is ready for user-sys-

tem handling. The LAPD Receiver will inform the Mi-

croprocessor/Microcontroller and the external circuit-

ry by:

• Generating a LAPD Message Frame Received

interrupt to the Microprocessor. The purpose of

this interrupt is to let the Microprocessor know that

the Receive LAPD Message buffer contains a new

PMDL Message that needs to be read and pro-

cessed. When the LAPD Receiver generates this

interrupt, it will set bit 0 (RxLAPD Interrupt Status)

within the Rx E3 LAPD Control Register to “1” as

depicted below.

)

• Setting Bit 1 (End of Message) within the Rx E3

LAPD Status Register, to “1” as depicted below.

In summary, Figure 143 presents a flow chart depict-

ing how the LAPD Receiver functions.

TABLE 62: THE RELATIONSHIP BETWEEN THE CONTENTS OF RXLAPDTYPE[1:0] BIT-FIELDS AND THE PMDL

MESSAGE TYPE/SIZE

RXLAPDTYPE[1:0]

PMDL MESSAGE TYPE

PMDL MESSAGE SIZE

Test Signal Identification

76 Bytes

Idle Signal Identification

76 Bytes

CL Path Identification

76 Bytes

ITU-T Path Identification

82 Bytes

RXE3 LAPD CONTROL REGISTER (ADDRESS = 0X18

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

Not Used

RxLAPD

Enable

RxLAPD

Interrupt Enable

RxLAPD

Interrupt Status

R/W

RUR

00000

RXE3 LAPD STATUS REGISTER (ADDRESS = 0X19)

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

Not Used

RxABORT

RxLAPDType[1:0]

RxCR

Type

RxFCS

Error

End of

Message

Flag

Present

0000

010

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