XRT7250 datasheet(154/463 Pages) EXAR

154 / 463 page

áç

DS3/E3 FRAMER IC

XRT7250

REV. 1.1.1

135

Operation of the Transmit Payload Data Input In-

terface

The Transmit Payload Data Input Interface is ex-

tremely flexible, in that it permits the user to make the

following configuration options.

• The Serial or the Nibble-Parallel Interface Mode

• The Loop-Timing or the TxInClk (Local Timing)

Mode

Further, if the XRT7250 has been configured to oper-

ate in the TxInClk (Local Timing) mode, then the user

has two additional options.

• The XRT7250 functions as the Frame Master (e.g.,

it dictates when the Terminal Equipment will initiate

the transmission of data within a new DS3 frame).

• The XRT7250 functions as the Frame Slave (e.g.,

the Terminal Equipment will dictate when the

XRT7250 initiates the transmission of a new DS3

frame).

Given these three set of options, the Transmit Termi-

nal Input Interface can be configured to operate in

one of the six (6) following modes.

• Mode 1 - Serial/Loop-Timed Mode

• Mode 2 - Serial/Local-Timed/Frame Slave Mode

• Mode 3 - Serial/Local-Timed/Frame Master Mode

• Mode 4 - Nibble/Loop-Timed Mode

• Mode 5 - Nibble/Local-Timed/Frame Slave Mode

• Mode 6 - Nibble/Local-Timed/Frame Master Mode

Each of these modes are described, in detail, below.

4.2.1.1

Mode 1 - The Serial/Loop-Timing Mode

The Behavior of the XRT7250

If the XRT7250 has been configured to operate in this

mode, then the XRT7250 will behave as follows.

A. Loop-Timing (Uses the RxLineClk signal as the

Timing Reference)

Since the XRT7250 is configured to operate in the

loop-timed mode, the Transmit Section (of the

XRT7250) will use the RxLineClk input clock signal

(e.g., the Recovered Clock signal, from the LIU) as its

timing source. When the XRT7250 is operating in

this mode it will do the following.

1. It will ignore any signal at the TxInClk input pin.

2. The XRT7250 will output a 44.736MHz clock sig-

nal via the RxOutClk output pin. This clock signal

functions as the Transmit Payload Data Input

Interface block clock signal.

3. The XRT7250 will use the rising edge of the

RxOutClk signal to latch in the data residing on

the TxSer input pin.

B. Serial Mode

The XRT7250 will accept the DS3 payload data from

the Terminal Equipment, in a serial-manner, via the

TxSer input pin The Transmit Payload Data Input In-

terface block will latch this data into its circuitry, on the

rising edge of the RxOutClk output clock signal.

C. Delineation of outbound DS3 frames

The XRT7250 will pulse the TxFrame output pin

"High" for one bit-period coincident with the XRT7250

processing the last bit of a given DS3 frame.

D. Sampling of Payload Data, from the Terminal

Equipment

In Mode 1, the XRT7250 will sample the data at the

TxSer input, on the rising edge of RxOutClk.

Interfacing the Transmit Payload Data Input Inter-

face block (of the XRT7250) to the Terminal Equip-

ment for Mode 1 Operation

TxFrameRef

Input

Transmit Frame Reference Input:

The XRT7250 permits the user to configure the Transmit Section to use this input pin as a

frame reference. If the user makes this configuration selection, then the Transmit Section will

initiate its transmission of a new DS3 frame, upon the rising edge of this signal.

The purpose of this input pin is to permit the Terminal Equipment to maintain Transmit DS3

Framing alignment control over the XRT7250.

RxOutClk

Output Loop-Timed Timing Reference Clock Output pin:

The Transmit Section of the XRT7250 can be configured to use the RxLineClk signal as the

Timing Reference (e.g., loop-timing). If the user has made this configuration selection, then

the XRT7250 will:

• Output a 44.736 MHz clock signal via this pin, to the Terminal Equipment.

• Sample the data on the TxSer input pin, upon the rising edge of this clock signal.

TABLE 18: LISTING AND DESCRIPTION OF THE PINS ASSOCIATED WITH THE TRANSMIT PAYLOAD DATA INPUT

INTERFACE

SIGNAL NAME

TYPE

DESCRIPTION

XRT7250 Datasheet(PDF) 154 Page - Exar Corporation

XRT7250 Datasheet(HTML) 154 Page - Exar Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL