Small Footprint RMII 10/100 Ethernet Transceiver with HP Auto-MDIX Support
Datasheet
Table 3.4 MODE[2:0] Bus
DEFAULT REGISTER BIT VALUES
MODE[2:0]
MODE DEFINITIONS
REGISTER 0
[13,12,10,8]
REGISTER 4
[8,7,6,5]
000
001
010
10Base-T Half Duplex. Auto-negotiation disabled.
10Base-T Full Duplex. Auto-negotiation disabled.
0000
0001
1000
N/A
N/A
N/A
100Base-TX Half Duplex. Auto-negotiation
disabled.
CRS is active during Transmit & Receive.
011
100
100Base-TX Full Duplex. Auto-negotiation disabled.
CRS is active during Receive.
1001
1100
N/A
100Base-TX Half Duplex is advertised. Auto-
negotiation enabled.
CRS is active during Transmit & Receive.
0100
101
110
Repeater mode. Auto-negotiation enabled.
100Base-TX Half Duplex is advertised.
CRS is active during Receive.
1100
N/A
0100
N/A
Power Down mode. In this mode the transceiver will
wake-up in Power-Down mode. The transceiver
cannot be used when the MODE[2:0] bits are set to
this mode. To exit this mode, the MODE bits in
Register 18.7:5(see Section 4.2.9, "Special Modes
Register," on page 57) must be configured to some
other value and a soft reset must be issued.
111
All capable. Auto-negotiation enabled.
X10X
1111
The MODE[2:0] hardware configuration pins are multiplexed with other signals as shown in Table 3.5.
Table 3.5 Pin Names for Mode Bits
MODE BIT
PIN NAME
MODE[0]
MODE[1]
MODE[2]
RXD0/MODE0
RXD1/MODE1
CRS_DV/MODE2
3.7.3
REGOFF: Internal +1.2V Regulator Configuration
The incorporation of flexPWR technology provides the ability to disable the internal +1.2V regulator.
When the regulator is disabled, an external +1.2V must be supplied to the VDDCR pin. Disabling the
internal +1.2V regulator makes it possible to reduce total system power, since an external switching
regulator with greater efficiency (versus the internal linear regulator) can be used to provide +1.2V to
the transceiver circuitry.
Note: Because the REGOFF configuration strap shares functionality with the LED1 pin, proper
consideration must also be given to the LED polarity. Refer to Section 3.8.1.1, "REGOFF and
LED1 Polarity Selection," on page 37 for additional information on the relation between
REGOFF and the LED1 polarity.
Revision 1.4 (08-23-12)
32
SMSC LAN8720A/LAN8720Ai
DATASHEET
SMSC [ SMSC CORPORATION ]
