Datasheet

Micrel, Inc.
KSZ8081MNX/KSZ8081RNB
August
19, 2015 30
Revision 1.4
Table 5. MII Management Frame Format for the KSZ8081MNX/RNB
Preamble
Start of
Frame
Read/Write
OP Code
PHY Address
Bits [4:0]
REG Address
Bits [4:0]
TA
Data
Bits [15:0]
Idle
Read
32 1’s 01 10 00AAA RRRRR Z0 DDDDDDDD_DDDDDDDD Z
Write
32 1’s 01 01 00AAA RRRRR 10 DDDDDDDD_DDDDDDDD Z
Interrupt (INTRP)
INTRP (Pin 21) is an optional interrupt signal that is used to inform the external controller that there has been a status
update to the KSZ8081MNX/RNB PHY register. Bits [15:8] of Register 1Bh are the interrupt control bits to enable and
disable the conditions for asserting the INTRP signal. Bits [7:0] of Register 1Bh are the interrupt status bits to indicate
which interrupt conditions have occurred. The interrupt status bits are cleared after reading Register 1Bh.
Bit [9] of Register 1Fh sets the interrupt level to active high or active low. The default is active low.
The MII management bus option gives the MAC processor complete access to the KSZ8081MNX/RNB control and status
registers. Additionally, an interrupt pin eliminates the need for the processor to poll the PHY for status change.
HP Auto MDI/MDI-X
HP Auto MDI/MDI-X configuration eliminates the need to decide whether to use a straight cable or a crossover cable
between the KSZ8081MNX/RNB and its link partner. This feature allows the KSZ8081MNX/RNB to use either type of
cable to connect with a link partner that is in either MDI or MDI-X mode. The auto-sense function detects transmit and
receive pairs from the link partner and assigns transmit and receive pairs to the KSZ8081MNX/RNB accordingly.
HP Auto MDI/MDI-X is enabled by default. It is disabled by writing a ‘1’ to Register 1Fh, Bit [13]. MDI and MDI-X mode is
selected by Register 1Fh, Bit [14] if HP Auto MDI/MDI-X is disabled.
An isolation transformer with symmetrical transmit and receive data paths is recommended to support Auto MDI/MDI-X.
Table 6 shows how the IEEE 802.3 Standard defines MDI and MDI-X.
Table 6. MDI/MDI-X Pin Definition
MDI MDI-X
RJ-45 Pin Signal RJ-45 Pin Signal
1 TX+ 1 RX+
2
TX−
2
RX−
3 RX+ 3 TX+
6
RX−
6
TX−