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10/100 Mbps Ethernet Controller Family Open Source Software Developer Manual 119
Physical Layer Interface
The individual registers are defined in the following subsections using the following conventions:
R: Read
W: Write
RO: Read only
SC: Self clearing
Note: The default values listed for the 82555 registers also apply to the registers in the embedded PHY
modules of the 82558 and 82559.
7.2.1 Control Register: Register 0
The Control register provides control over the PHY functions.
Bit Name R / W Description Default
15 Reset
R/W
SC
The Reset bit causes the device to reset to its
default state. Configuration settings that are issued
with the Reset bit will not be accepted, and the
device is set to the default state when the reset is
completed. This bit should set by itself. For write
operations to other bits of the Control register,
software should ensure the reset bit is not set.
Resetting the PHY also re-starts Auto-Negotiation.
1 = PHY reset
0 = normal operation
0
14 Loopback R/W
1 = loopback mode
0 = normal operation
0
13 10/100 R/W
1 = 100 Mbps
0 = 10 Mbps
1
12 Auto-Negotiation Enable R/W
The Auto-Negotiation settings take precedence
over forced speed and duplex settings. In other
words, if both speed and duplex are set, Auto-
Negotiation will override these settings. To
successfully enable forced speed and duplex, Auto-
Negotiation must be disabled through this bit and
the Restart Auto Configuration bit (bit 9) must equal
0.
1 = Enable Auto-Negotiation
0 = Disable Auto-Negotiation
1
11 Power Down R/W
1 = power down
0 = normal operation
0
10 Isolate R/W
1 = electrically isolate PHY from MII
0 = normal operation
0
9
Restart Auto
Configuration
R/W
SC
The Auto-Negotiation settings take precedence
over forced speed and duplex settings. In other
words, if both speed and duplex are set, Auto-
Negotiation will override these settings. To
successfully enable forced speed and duplex, Auto-
Negotiation must be disabled through this bit and
the Auto-Negotiation Enable bit (bit 12) must equal
0.
1= Restart the auto negotiation
0 = Normal operation
0