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0.14
Loopback
1 = loopback mode switched on
0 = loopback mode switched off
0.13
Rate Selection
(least−significant bit
[LSB])
0.6 0.13
1 1 reserved
1 0 1000 Mbps
0 1 100 Mbps
0 0 10 Mbps
0.12
Autonegotiation Enable
1 = autonegotiaton enabled
0 = autonegotiation disabled
0.11
Power Down
1 = power down
0 = normal down
0.10
Isolated
1 = PHY electrically isolated
from media−independent
interface (MII)
0 = normal mode
0.9
Restart Autonegotiation
1 = restart the autonegotiation
process
0 = normal mode
0.8
Duplex Mode
1 = full−duplex
0 = half−duplex
0.7
Collision Test
1 = collision (COL) signal test
active
0 = COL signal test switched off
0.6
Rate Selection
(most−significant bit
[MSB])
See bit 0.13
The register bits relevant to this document include 0.13, 0.12, 0.8, and 0.6. The other register bits are
documented in the IEEE 802.3u specification. Based on IEEE 802.3u, in order to manually set the rate
(speed), the autonegotiation bit, 0.12, must be set to a value of 0. As a result, autonegotiation must be disabled
in order to manually set the speed and duplex. If the autonegotiation bit 0.12 is set to a a value of 1, bits 0.13
and 0.8 have no significance, and the link uses autonegotiation to determine the speed and duplex. When
autonegotiation is disabled, the default value for duplex is half−duplex, unless the 0.8 is programmed to 1,
which represents full−duplex.
Based on IEEE 802.3u, it is not possible to manually configure one link partner for 100 Mbps, full−duplex
and still autonegotiate to full−duplex with the other link partner. If you attempt to configure one link partner
for 100 Mbps, full−duplex and the other link partner for autonegotiation, it results in a duplex mismatch. This
is because one link partner autonegotiates and does not see any autonegotiation parameters from the other link