AM79C971VCW Advanced Micro Devices, AM79C971VCW Datasheet - Page 80

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

configure the network port and the Am79C971 control-
ler will always defer to the software driver. When The
ASEL is set to 0, the software driver should then con-
figure the ports with PORTSEL (CSR15, bits 7-8). The
GPSI does not participate in the automatic selection
process and should be manually configured with the
PORTSEL bits. If FDEN (BCR9, bit 0) is set to 1 or
DLNKST (CSR15, bit 12) is set to 1, the Network Port
Manager will continue to select the active network port,
but the internal T-MAU will not auto-negotiate the net-
work port. Instead, if FDEN (BCR9, bit 0) is set to 1, the
internal T-MAU will come up as a full-duplex T-MAU port
if link beats are found. If DLNKST (CSR15, bit 12) is set
to 1 and the internal T-MAU is active, the T-MAU will be
in a link pass state regardless of link beat.
Note:
PORTSEL be used when trying to manually configure
a specific network port.
In order to manually configure the External PHY, the
recommended procedure is to force the PHY configu-
rations when Auto-Negotiation is not enabled. Set the
DANAS bit (BCR32, bit 7) to turn off the Network Port
Manager. Then write again to BCR32 with the DANAS
and XPHYANE (BCR32, bit 5) bits cleared, together
with the XPHYFD (BCR32, bit 4) and XPHYSP
(BCR32, bit 3) bits set to the desired configuration. The
Network Port Manager will send a few frames to vali-
date the configuration.
If FCON (BCR32, bit 0) is set to 1, this bit will force the
internal Network Port Manager into Fast Configuration
Mode. During this mode, the Network Port Manager will
not attempt to start Auto-Negotiation on the internal as
well as the external PHY. Instead, it will rely on link in-
tegrity tests for link pass state. This will accelerate the
automatic port selection on the Am79C971 controller.
The Network Port Manager in Fast Configuration Mode
will start with the external PHY if one is detected. If the
link does not come up, the Network Port Manager will
enable the internal 10BASE-T MAU. If the internal port
also does not come up, the Network Port Manager will
continue to search the MII and the internal T-MAU ports
while enabling the internal AUI por t. The FCON
(BCR32, bit 0) should only be used if the network is ex-
periencing difficulty and is not stable.
CAUTION: The Network Port Manager utilizes the
PHYADD (BCR33, bits 9-5) to communicate with the
external PHY during the automatic port selection pro-
cess. The PHYADD is copied into a shadow register
after the Am79C971 controller has read the configura-
tion information from the EEPROM. Extreme care must
be exercised by the host software not to access BCR33
during this time. A read of PVALID (BCR19, bit 15) be-
fore accessing BCR33 will guarantee that the PHYADD
has been shadowed.
Am79C972’s Automatic Network Port selection mecha-
nism falls within the following three general categories:
80
It is highly recommended that ASEL and
Am79C971
Automatic Network Selection: External PHY Not
Present
The first case occurs when the MIIPD (BCR32, bit 14)
bit is 0. This indicates that there is no external PHY at-
tached to Am79C971 controller’s MII. The Am79C971
controller’s Network Port Manager will start the internal
Auto-Negotiation 10BASE-T MAU. If the Auto-Negotia-
tion 10BASE-T MAU fails to respond within a specific
time frame, then the Am79C971 controller will enable
the AUI. Auto-Negotiation FAST Link Pulses are still
being sent and the Auto-Negotiation 10BASE-T MAU is
still running. At that point, the active link can switch
back to the 10BASE-T MAU when Link Pulses or FAST
Link Pulses are detected. The only way to disable the
Auto-Negotiation process without using FDEN or
DLNKST is to enable the DANAS (BCR32, bit 7) bit or
to write to the internal/external PHYs MII control regis-
ter and disable Auto-Negotiation when the internal Net-
work Port Manager is disabled.
Automatic Network Selection: External PHY
Present but Not Auto-Negotiable
The second case occurs when the MIIPD (BCR32, bit
14) bit is 1. This indicates that there is an external PHY
attached to Am79C971 controller’s MII. If more than
one external PHY is attached to the MII Management
Interface, then the DANAS (BCR32, bit 7) bit must be
set to 1 and then all configuration control should revert
to software. The Am79C971 controller will read the reg-
ister of the external PHY to determine its status and
network capabilities. See Appendix E, Auto Negotiation
Registers, for the bit descriptions of the MII Status reg-
ister. If the external PHY is not Auto-Negotiation capa-
ble and/or the XPHYANE (BCR32, bit 5) bit is set to 0,
then the Network Port Manager will match up the exter-
nal PHY capabilities with the XPHYFD (BCR 32, bit 4)
and the XPHYSP (BCR32, bit 3) bits programmed from
the EEPROM. The Am79C971 controller will then pro-
gram the external PHY with those values. A new read
of the external PHYs MII Status register will be made to
see if the link is up. If the link does not come up as pro-
grammed after a specific time, the Am79C971 control-
ler will fail the external PHY link and start the internal
PHY process as described above. The Am79C971
controller will only start the external PHY link if the in-
ternal link has failed. If both links have failed, the AUI is
enabled but the Network Port Manager will still query
the internal and external PHYs for active links.
Automatic Network Selection: External PHY
Present and Auto-Negotiable
The third case occurs when the MIIPD (BCR32, bit 14)
bit is 1. This indicates that there is an external PHY at-
tached to Am79C971 controller’s MII. If more than one
External PHY Not Present
External PHY Present but Not Auto-Negotiable
External PHY Present and Auto-Negotiable