
LXT9785 and LXT9785E Advanced 8-Port 10/100 Mbps PHY Transceivers
Datasheet
121
Document Number: 249241
Revision Number: 010
Revision Date: 30-May-2006
physical connection, a specific protocol that runs across the connection, and an internal set of
addressable registers. Some registers are required and their functions are defined by the IEEE
802.3 specification. Additional registers allow for expanded functionality. Specific bits in the
registers are referenced using an “X.Y” notation, where X is the register number (0-32) and Y is
the bit number (0-15).
The physical interface consists of a data line (MDIO) and clock line (MDC). Operation of this
interface is controlled by the MDDIS input pin. When MDDIS is High, all the MDIOs are
completely disabled. The Hardware Control Interface provides primary configuration control.
When MDDIS is Low, the MDIO port is enabled for both read and write operations and the
Hardware Control Interface is not used.
Note:
The BGA15 package does not support the MDDIS pin.
The protocol allows one controller to communicate with multiple LXT9785/LXT9785E chips. Pins
ADD_<4:0> determine the base address. Each port adds its port number to the base address to
obtain its port address as shown in
Figure 11.
The BGA15 package uses a similar scheme where the ADD_[2:0] bits internally set to 0 and the
ADD_[4:3] bits are used to select from four base addresses (0x00000b, 0x01000b, 0x10000b, or
0x11000b.
Figure 9. Management Interface Read Frame Structure
Figure 10. Management Interface Write Frame Structure
MDC
MDIO
(Read)
32 "1"s
011
0
Preamble
ST
Op Code
PHY Address
Turn
Around
Z0
A4
A3
A0
R4
R3
R0
Register Address
D15
D14
D1
Data
Write
Read
D15
D14
D1
D0
Idle
High Z
MDC
MDIO
(Write)
32 "1"s
0101
Preamble
ST
Op Code
PHY Address
Turn
Around
1
0
A4
A3
A0
R4
R3
R0
Register Address
D15
D14
D1
D0
Data
Idle
Write