XRT7250 datasheet(168/463 Pages) EXAR

168 / 463 page

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DS3/E3 FRAMER IC

XRT7250

REV. 1.1.1

149

3. Interface the XRT7250, to the Terminal Equip-

ment, as illustrated in Figure 54.

4.2.2

The Transmit Overhead Data Input Inter-

face

Figure 56 presents a simple illustration of the Trans-

mit Overhead Data Input Interface block within the

XRT7250.

The DS3 Frame consists of 4760 bits. Of these bits,

4704 bits are payload bits and the remaining 56 bits

are overhead bits. The XRT7250 has been designed

to handle and process both the payload type and

overhead type bits for each DS3 frame. Within the

Transmit Section within the XRT7250, the Transmit

Payload Data Input Interface has been designed to

handle the payload data. Likewise, the Transmit

Overhead Data Input Interface has been designed to

handle and process the overhead bits.

The Transmit Section of the XRT7250 generates or

processes the various overhead bits within the DS3

frame, in the following manner.

The Frame Synchronization Overhead Bits (e.g.,

the F and M bits)

The F and M bits are always internally generated by

the Transmit Section of the XRT7250. These over-

head bits are used (by the Remote Terminal Equip-

ment) for Frame Synchronization purposes. Hence,

the user cannot insert his/her value for the F and M

bits into the outbound DS3 data stream, via the

Transmit Overhead Data Input Interface. Any attempt

to externally insert values for the “F” and “M” bits, will

be ignored by the Transmit Overhead Data Input In-

terface"High" block.

The Performance Monitoring Overhead Bits (P

and CP Bits)

The P-bits are always internally generated by the

Transmit Section of the XRT7250. The “P” bits are

used by the Remote Terminal Equipment to perform

FRAMER OPERATING MODE REGISTER (ADDRESS = 0X00)

BIT 7BIT 6BIT 5BIT 4BIT 3BIT2

BIT 1

BIT 0

FIGURE 56. SIMPLE ILLUSTRATION OF THE TRANSMIT OVERHEAD DATA INPUT INTERFACE BLOCK

Transmit

Overhead

Data Input

Interface Block

Transmit

Overhead

Data Input

Interface Block

TxOHFrame

TxOHEnable

TxOH

TxOHClk

TxOHIns

To Transmit DS3 Framer Block

XRT7250 Datasheet(PDF) 168 Page - Exar Corporation

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