Draft 6/5/00
2-28
Functional Description
Copyright 2000 by LSI Logic Corporation. All rights reserved.
2.2.9.2 Receiver
The FX receiver:
Converts the differential ECL inputs on the FXI+/- pins to a digital bit
stream
Validates the data on FXI+/- with the SD/FXDISn input pin
Enable or disables the FX interface with the SD/FXDISn pin.
The FX receiver meets all requirements defined in IEEE 802.3.
The input to the FXI+/- pins can be directly driven from a fiber optic
transceiver and first goes to a comparator. The comparator compares the
input waveform against the internal ECL threshold levels to produce a
low jitter serial bit stream with internal logic levels. The data from the
comparator output is then passed to the clock and data recovery block,
provided that the signal detect input, SD/FXDISn, is asserted.
Signal Detect –
The FX receiver has a signal detect input pin,
SD/FXDISn, which indicates whether the incoming data on FXI+/- is valid
or not. The SD/FXDISn input can be driven directly from an external fiber
optic transceiver and meets all requirements defined in the IEEE 802.3
specifications.
The SD/FXDISn input goes directly to a comparator. The comparator
compares the input waveform against the internal ECL threshold level to
produce a digital signal with internal logic levels. The output of the signal
detect comparator then goes to the link integrity and squelch blocks. If
the SD/FXDISn input is asserted, the device is placed in the Link Pass
state and the input data on FXI+/- is determined to be valid. If the
SD/FXDISn input is deasserted, the device is placed in the Link Fail state
and the input data on FXI+/- is determined to be invalid.
The SD_THR pin adjusts the ECL trip point of the SD/FXDISn input.
When the SD_THR pin is tied to a voltage between GND and GND +
0.45V, the trip point of the SD/FXDISn ECL input buffer is internally set
to VDD
1.3 V. When the SD_THR pin is set to a voltage greater than
GND + 0.85 V, the trip point of the SD/FXDISn ECL input buffer is set to
the voltage that is applied to the SD_THR pin. The trip level for the
SD/FXDISn input buffer must be set to VDD
1.3 V. Having external
control of the SD/FXDISn buffer trip level with the SD_THR pin allows
this trip level to be referenced to an external supply, which facilitates