HFBR-4663 Просмотр технического описания (PDF) - HP => Agilent Technologies

Номер в каталоге

Компоненты Описание

производитель

HFBR-4663

Single Chip 10BASE-FL Transceiver

HP => Agilent Technologies 

correct RTSET resistor:

( ) RTSET= –5–2––m––A l62 Ω

IOUT

The transmitter enters the idle

state when it detects start of idle

on Tx+ and Tx- input pins. After

detecting the start of idle, the

transmitter switches to a 1 MHz

output idle signal.

VCC

51 Ω

51 Ω

51 Ω

RTSET = 560 Ω

IOUT = 15.9 mA

ECL

VCCTx

TxOUT

Figure 3. Converting Optical LED Driver Output to Differential ECL.

The output current is switched

through the TxOUT pin during the

on cycle and the VCCTx pin during

the off cycle as shown in figure 2.

Since the sum of the current in

these two pins is constant, VCCTx

should be connected as close as

possible to the VCC connection for

the LED.

If not driving an optical LED

directly, a differential output can

be generated by tying resistors

from VCCTx and TxOUT to VCC as

shown in Figure 3. The minimum

voltage on these two pins should

not be less than VCC - 2 V.

VCCTx

TxOUT

IOUT

Figure 2. Fiber Optic LED Driver

Structure.

Reception

The input to the transceiver

comes from a fiber optic receiver

as shown in figure 1. At the start

of packet reception no more than

2.7 bits are received from the

fiber cable and not transmitted

onto the DI circuit. The receive

squelch will reject frequencies

lower than 2.51 MHz.

While in the unsquelch state, the

receive squelch circuit looks for

the start of idle signal at the end

of the packet. Start of idle occurs

when the input signal remains idle

for more than 160 ns. When start

of idle is detected, the receive

squelch circuit returns to the

squelch state and the start of idle

signal is output on the DI circuit

(Rx+, Rx-).

Collision

Whenever the receiver and the

transmitter are active at the same

time the chip will activate the

collision output, except when

loopback is disabled (LBDIS =

Vcc). The collision output is a

differential square wave matching

the AUI specifications and

capable of driving a 78 Ω load.

The frequency of the square wave

is 10 MHz ± 15% with a 60/40 to

40/60 duty cycle. The collision

oscillator also is activated during

SQE Test and jabber.

Loopback

The loopback function emulates a

10BASE-T transceiver whereby

the transmit data sent by the DTE

is looped back over the AUI

receive pair. Some LAN

controllers use this loopback

information to determine whether

a MAU is connected by

monitoring the carrier sense while

transmitting. The software can

use this loopback information to

determine whether a MAU is

connected to the DTE by

checking the status of carrier

sense after each packet

transmission.

When data is received by the chip

while transmitting, a collision

condition exits. This will cause

the collision oscillator to turn on

and the data on the DI pair will

follow VIN+, VIN-. After a collision

is detected, the collision oscillator

will remain on until either DO or

VIN+, VIN- go idle.

Loopback can be disabled by

strapping LBDIS to VCC. In this

mode the chip operates as a full

duplex transmitter and receiver,

and collision detection is disabled.

A loopback through the

transceiver can be accomplished

by tying the fiber transmitter to

the receiver.

85

Share Link: