ICS1889 datasheet(6/35 Pages) ICST

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ICS1889

Line Transmitter

The LineTransmitter output pair is a differential positive ECL

(PECL) interface designed to connect directly to a standard

fiber optic transceiver. The differential driver for the transmit

signal is a programmable current source designed for resistive

termination. Using an external resistor connected to the IPRG

pin, the output current may be preset.

The differential driver for the TX ± is current mode and is

designed to drive resistive terminations in a complementary

fashion. The output is current-sinking only, with the amount

of sink current programmable via the IPRG1 pin. The sink

current is equal to four times the IPRG1 current. For most

applications, an 910Ω resistor from VDD to IPRG1 will set

the current to the necessary precision.

The TX± pins are incapable for sourcing current, so VOH must

be set by the ratios of the Thevenin termination resistors for

each of the lines. R1 is a pull-up resistor connected from the

PECL output to VDD. R2 is a pull-down resistor connected

from the PECL output to VSS. R1 and R2 are electrically in

parallel from an AC standpoint. If we pick a target impedance

of 50Ω for our transmission line impedance, a value of 62Ω

for R1 and a value of 300Ω for R2 would yield a Thevenin

equivalent characteristic impedance of 49.7Ω and a VOH

value of VDD -.88 volts, compatible with PECL circuits.

To set a value for VOL, we must determine a value for Iprg

that will cause the output FETs to sink an appropriate current.

We desire VOL to be VDD -1.81 or greater. Setting up a sink

current of 19 milliamperes would guarantee this through our

output termination resistors. As this is controlled by

4/1 current mirror, 4.75mA into Iprg should set this current

properly. A 910Ω resistor from VDD to Iprg should work fine.

Line Receiver

The Line Receiver is a differential input pair designed to

interface directly to a standard fiber optic transceiver. It is a

differential PECL input buffer.

Signal Error Detector

The ICS1889 Signal Error Detector is part of the clock

recovery PLL. It detects a Receive Signal Error if no receive

signal is received and detects a PLL Lock Error if the PLL is

unable to lock on to the receive channel signal. A receive

channel error is defined as the loss of receive signal or the loss

of PLL lock.

Remote Fault Signaling

Remote fault signaling allows a node to indicate receive

channel errors to its Link Partner using its transmit channel.

When used by both nodes on a link segment, the integrity of

both the transmit and receive channels can be verified.

Since 100Base-FX systems do not use auto-negotiation, an

alternative, in-band signaling scheme is used to signal remote

fault conditions. This scheme, Far End Fault Indication, relies

on the characteristics of the quiescent state, (a continuous

IDLE stream). The IDLE stream is a continuous stream of

logic ones and a carrier is defined as the receipt of two

noncontiguous logic zeroes. A Far End Fault is signaled with

84 logic ones followed by one logic zero, with the pattern

repeated at least three times.

A Far End Fault will be signaled under three conditions; the

first is when no activity is received from the Link Partner,

since this can indicate a broken receive wire. The second is

when the clock recovery circuit detects a Receive Signal Error

or PLL Lock Error. The third is when a management entity

sets the Transmit Far End Fault bit (16:3).

Far End Fault signaling continues until the condition causing

the fault ceases.

Far End Fault Detection

The Far End Fault detector monitors the receive data serial bit

stream looking for a repetitive pattern of 84 logic ones

followed by a logic zero. Non-ICS1889 PHYs may have

different definitions of what constitutes a remote fault.

However, an ICS1889 will always respond to the in-band

error signaling scheme. If the ICS1889 detects three

consecutive patterns described above, it will signal a far end

fault to the Link Monitor.

Link Monitor

If the Link Monitor receives a far end fault indication or a

local receive channel error, it causes the ICS1889 to enter the

IDLE mode, isolate the MII and assert the Link Status bit in

the Status Register. Once the far end fault condition is de-

asserted, the Link Monitor will return to the Link OK

condition if the local receive channel is clear of errors. Once

detected, a receive channel error signal will be indicated from

330 to 1000 microseconds.

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