AFCT-701ASDZ datasheet(3/18 Pages) AVAGO

3 / 18 page

Figure 1. Transceiver functional diagram

Transmit Fault (TX_FAULT)

A catastrophic laser fault will activate the transmitter

signal, TX_FAULT, and disable the laser. This signal is

an open collector output (pull-up required on the host

board). A low signal indicates normal laser operation and

a high signal indicates a fault. A fault is defined as laser

power below or above the specified IEEE 802.3ae speci-

fied min/max range. The TX_FAULT will be latched high

when a laser fault occurs and is cleared by toggling the

TX_DISABLE input or power cycling the transceiver. The

transmitter fault condition can also be monitored via the

two-wire serial interface (address A2, byte 110, bit 2).

LIGHT FROM FIBER

LIGHT TO FIBER

PHOTO-DETECTOR

RECEIVER

AMPLIFICATION

& QUANTIZATION

RD+ (RECEIVE DATA)

RD– (RECEIVE DATA)

RX_LOS

DFB

TRANSMITTER

LASER

DRIVER &

SAFETY

CIRCUITRY

TX_DISABLE

TD+ (TRANSMIT DATA)

TD– (TRANSMIT DATA)

TX_FAULT

ELECTRICAL INTERFACE

SDA

SCL

MOD-ABS

CONTROLLER & MEMORY

OPTICAL INTERFACE

RS0

RS1

Transmitter Section

The transmitter section includes the Transmitter Opti-

cal Sub-Assembly (TOSA) and laser driver circuitry. The

TOSA, containing an Avago designed and manufactured

1310 nm DFB light source, is located at the optical inter-

face and mates with the LC optical connector. The TOSA

is driven by an IC which uses the incoming differential

high speed logic signal to modulate the laser diode driv-

er current. This Tx laser driver circuit regulates the optical

power at a level within the specified range.

Transmit Disable (TX_DISABLE)

The AFCT-701ASDZ accepts an LVTTL compatible trans-

mit disable control signal input which shuts down the

transmitter optical output. A high signal implements this

function while a low signal allows normal transceiver op-

eration. In the event of a fault (e.g. eye safety circuit ac-

tivated), cycling this control signal resets the module as

depicted in Figure 5. An internal pull up resistor disables

the transceiver transmitter until the host pulls the input

low. TX_DISABLE can also be asserted via the two-wire

interface (address A2h, byte 110, bit 6) and monitored

(address A2h, byte 110, bit 7).

The contents of A2h, byte 110, bit 6 are logic OR’d with

hardware TX_DISABLE (contact 3) to control transmitter

operation. The normal behavior of this feature is to reset

a TX disabled transceiver to TX enabled when it is power

cycled or hot-plugged.

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