AM79C973VCW datasheet(87/304 Pages) AMD

87 / 304 page

Am79C973/Am79C975

P R E L I M INARY

nals and to mitigate carrier fade in the event of worst

case signal attenuation and crosstalk noise conditions.

Figure 38. 10BASE-T Transmit and Receive Data

Paths

Twisted Pair Interface Status

The Am79C973/Am79C975 device will power up in the

Link Fail state. The Auto-Negotiation algorithm will

apply to allow it to enter the Link Pass state.

In the Link Pass state, receive activity which passes the

pulse width/amplitude requirements of the RX± inputs,

will cause the PCS Control block to assert Carrier

Sense (CRS) signal at the internal MII interface. Colli-

sion would cause the PCS Control block to assert Car-

rier Sense (CRS) and Collision (COL) signal at the

internal MII. In the Link Fail state, this block would

cause the PCS Control block to de-assert Carrier

Sense (CRS) and Collision (COL).

In jabber detect mode, this block would cause the PCS

Control block to assert the COL pin at the MII, and

allow the PCS Control block to assert or de-assert the

CRS pin to indicate the current state of the RX± pair. If

there is no receive activity on RX±, this block would

cause the PCS Control block to assert only the COL pin

at the internal MII. If there is RX± activity, this block

would cause the PCS Control block to assert both COL

and CRS at the internal MII.

Collision Detect Function

Simultaneous activity (presence of valid data signals)

from both the internal encoder transmit function and

the twisted pair RX± pins constitutes a collision,

thereby causing the PCS Control block to assert the

COL pin at the internal MII.

Jabber Function

The Jabber function inhibits the 10BASE-T twisted pair

transmit function of the Am79C973/Am79C975 device

if the TX± circuits are active for an excessive period

(20-150 ms). This prevents one port from disrupting the

network due to a stuck-on or faulty transmitter condi-

tion. If the maximum transmit time is exceeded, the

data path through the 10BASE-T transmitter circuitry is

disabled (although Link Test pulses will continue to be

sent). The PCS Control block also asserts the COL pin

at the internal MII and sets the Jabber Detect bit in

the MENDEC stops, an unjab time of 250-750 ms will

elapse before this block causes the PCS Control block

to de-assert the COL indication and re-enable the

transmit circuitry.

When jabber is detected, this block will cause the PCS

control block to assert the COL pin and allow the PCS

Control block to assert or de-assert the CRS pin to in-

dicate the current state of the RX± pair. If there is no re-

ceive activity on RX±, this block causes the PCS

Control block to assert only the COL pin at the internal

MII. If there is RX± activity, this block will cause the

PCS Control block to assert both COL and CRS at the

internal MII.

Reverse Polarity Detect

The polarity for 10BASE-T signals is set by reception of

Normal Link Pulses (NLP) or packets. Polarity is

locked, however, by incoming packets only. The first

NLP received when trying to bring the link up will be ig-

nored, but it will set the polarity to the correct state. The

reception of two consecutive packets will cause the po-

larity to be locked, based on the polarity of the ETD. In

order to change the polarity once it has been locked,

the link must be brought down and back up again.

Auto-Negotiation

The object of the Auto-Negotiation function is to deter-

mine the abilities of the devices sharing a link. After ex-

changing abilities, the Am79C973/Am79C975 device

and remote link partner device acknowledge each

other and make a choice of which advertised abilities to

support. The Auto-Negotiation function facilitates an

ordered resolution between exchanged abilities. This

exchange allows both devices at either end of the link

to take maximum advantage of their respective shared

abilities.

Clock

Data

Manchester

Encoder

Clock

Data

Manchester

Decoder

Squelch

Circuit

RX Driver

TX Driver

21510D-43

AM79C973VCW Datasheet(PDF) 87 Page - Advanced Micro Devices

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