AM79C971VCW datasheet(79/265 Pages) AMD

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Am79C971

gotiation Registers, for the bit descriptions of the MII

Status Register. The contents of the latest read from

the external PHY will be stored in a shadow register in

the Auto-Poll block. The first read of the MII Status Reg-

ister will just be stored, but subsequent reads will be

compared to the contents already stored in the shadow

the MII Status Register, a MAPINT (CSR7,

bit 7) in-

terrupt will be generated on INTA if the MAPINTE

(CSR7, bit 6) is set to 1. The Auto-Poll features can be

disabled if software driver polling is required.

The Auto-Poll’s frequency of generating MII manage-

ment frames can be adjusted by setting of the APDW

bits (BCR32, bits 10-8). The delay can be adjusted

from 0 MDC periods to 2048 MDC periods. Auto-Poll by

default will only read the MII Status register in the ex-

ternal PHY.

Network Port Manager

The Am79C971 controller is unique in that it does not

require software intervention to control and configure

an external PHY attached to the MII. This was done to

ensure backwards compatibility with existing software

drivers. To the current software drivers, the Am79C971

controller will look and act like the PCnet-PCI II and will

interoperate with existing PCnet drivers from revision

2.5 upward. The heart of this system is the Network

Port Manager, which acts as an arbiter between all of

the possible automatically controllable physical con-

nections, including the external PHY and the internal

10BASE-T/AUI ports. See the section on Automatic

Network Port Selection for more details.

If the external PHY is present and is active, the Net-

work Port Manager will request status from the external

PHY by generating MII management frames. These

frames will be sent roughly every 900 ms. These

frames are necessary so that the Network Port Man-

ager can monitor the current active link and can select

a different network port if the current link goes down.

Auto-Negotiation

The Am79C971 controller implements the Auto-Nego-

tiation portion of the IEEE 802.3u specification for the

10BASE-T MAU. Auto-Negotiation attempts to auto-

matically configure the link between two link partners.

To accomplish this, the 10BASE-T MAU can send a

new link pulse train called Fast Link Pulses. These Fast

Link Pulses replace the current 10BASE-T Link Pulse.

The Fast Link Pulse are made up of a train of 17 clocks

alternating with 16 data fields for a total of 33 pulses.

The two link partners will send information in those 16

data positions between themselves. The primary infor-

mation sent is called the Base Code Link Word. See

Appendix E, Auto Negotiation Registers, for details on

the Auto-Negotiation Registers. The Am79C971 con-

troller will send in its Base Code Link Word the capabil-

ities of the internal PHY. The internal PHY is capable of

half- or full-duplex 10BASE-T. Through the external

PHY, the following capabilities are possible: 100BASE-

T4, 100BASE-TX Full-/Half-Duplex, and 10BASE-T

Full-/Half-Duplex. The capabilities are then sent to a

link partner that will also send its capabilities. Both

sides look to see what is possible and then they will

connect at the greatest possible speed and capability

according to the following table as defined in the IEEE

802.3u standard.

By default, the link partner must be at least 10BASE-T

half-duplex capable. The Am79C971 controller can au-

tomatically negotiate either internally or externally with

the network and yield the highest performance possible

without software support. See the section on Network

Port Manager for more details.

Auto-Negotiation goes further by providing a message-

based communication scheme called, Next Pages, be-

fore connecting to the Link Partner. This feature is not

supported in Am79C971 unless the DANAS (BCR32,

bit 10) is selected and the software driver is capable of

controlling the internal or external PHY.

A complete bit description of the MII and Auto-Negoti-

ation registers can be found in Appendix E.

Automatic Network Port Selection

The Am79C971 controller extends the PCnet-PCI II de-

vice’s automatic network port selection by adding the

MII port to the already existing 10BASE-T, and AUI

ports. If ASEL (BCR2, bit 0) is set to 1 and DANAS

(BCR 32, bit 7) is set to 0, then the Network Port Man-

ager will start to configure the external PHY if it detects

the external PHY on the MII Interface. If the external

PHY is not responding, the Network Port Manager will

try to resolve problems and to fail non-responding links

in a graceful manner, utilizing a large timer on the

Am79C971 controller to time-out links.

Automatic Network Selection: Exceptions

If ASEL (BCR2, bit 0) is set to 0 or DANAS (BCR 32, bit

7) is set to 1, then the Network Port Manager will dis-

continue actively trying to establish the connections. It

is assumed that the software driver is attempting to

Table 10.

Auto-Negotiation Capabilities

Network Speed

Physical Network Type

200 Mbps

100BASE-X, Full Duplex

100 Mbps

100BASE-T4, Half Duplex

100 Mbps

100BASE-X, Half Duplex

20 Mbps

10BASE-T, Full Duplex

10 Mbps

10BASE-T, Half Duplex

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