AM79C971VCW Advanced Micro Devices, AM79C971VCW Datasheet - Page 79

• Manufacturer Part Number: AM79C971VCW
• Description: PCnet-FAST Single-Chip Full-Duplex 10/100 Mbps Ethernet Controller for PCI Local Bus
• Manufacturer: Advanced Micro Devices

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
register. If there has been a change in the contents of
the MII Status Register, a MAPINT (CSR7,
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-
bit 7) in-
Am79C971
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
Network Speed
200 Mbps
100 Mbps
100 Mbps
Table 10. Auto-Negotiation Capabilities
20 Mbps
10 Mbps
Physical Network Type
100BASE-T4, Half Duplex
100BASE-X, Half Duplex
100BASE-X, Full Duplex
10BASE-T, Half Duplex
10BASE-T, Full Duplex
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