7.1.1 Basic Mode Control Register (BMCR)
Table 12. Basic Mode Control Register (BMCR), address 0x00
Bit
Bit Name
Default
Description
15
Reset
0, RW/SC
Reset:
1 = Initiate software Reset / Reset in Process.
0 = Normal operation.
This bit, which is self-clearing, returns a value of one until the reset
process is complete. The configuration is re-strapped.
14
Loopback
0, RW
Loopback:
1 = Loopback enabled.
0 = Normal operation.
The loopback function enables MII transmit data to be routed to the MII
receive data path.
Setting this bit may cause the descrambler to lose synchronization and
produce a 500 µs “dead time” before any valid data will appear at the
MII receive outputs.
13
12
Speed Selection
Strap, RW
Strap, RW
Speed Select:
When auto-negotiation is disabled writing to this bit allows the port
speed to be selected.
1 = 100 Mb/s.
0 = 10 Mb/s.
Auto-Negotiation
Enable
Auto-Negotiation Enable:
Strap controls initial value at reset.
1 = Auto-Negotiation Enabled - bits 8 and 13 of this register are ig-
nored when this bit is set.
0 = Auto-Negotiation Disabled - bits 8 and 13 determine the port speed
and duplex mode.
11
Power Down
0, RW
Power Down:
1 = Power down.
0 = Normal operation.
Setting this bit powers down the PHY. Only the register block is en-
abled during a power down condition. This bit is OR’d with the input
from the PWR_DOWN/INT pin. When the active low
PWR_DOWN/INT pin is asserted, this bit will be set.
10
9
Isolate
0, RW
Isolate:
1 = Isolates the Port from the MII with the exception of the serial man-
agement.
0 = Normal operation.
Restart Auto-
Negotiation
0, RW/SC
Restart Auto-Negotiation:
1 = Restart Auto-Negotiation. Re-initiates the Auto-Negotiation pro-
cess. If Auto-Negotiation is disabled (bit 12 = 0), this bit is ignored. This
bit is self-clearing and will return a value of 1 until Auto-Negotiation is
initiated, whereupon it will self-clear. Operation of the Auto-Negotiation
process is not affected by the management entity clearing this bit.
0 = Normal operation.
8
Duplex Mode
Strap, RW
Duplex Mode:
When auto-negotiation is disabled writing to this bit allows the port Du-
plex capability to be selected.
1 = Full Duplex operation.
0 = Half Duplex operation.
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