
Agere Systems Inc.
147
Data Sheet
July 2001
T8302 Internet Protocol Telephone
Advanced RISC Machine (
ARM
)
12 Ethernet 10/100 PHY(s)
(continued)
A specific set of registers and their contents
(see Table 127 on page 148)
defines the nature of the information
transferred across the MDIO interface. Frames transmitted on the MII station management interface will have the
frame structure shown in Table 126 below. The order of bit transmission is from left to right.
Note:
Reading and writing the
MII
management register
must be completed without interruption.
12.5.1 MII Management Frame Format
Table 126. MII Management Frame Format
R/W
R
W
PRE
1 . . . 1
1 . . . 1
ST
01
01
OP
10
01
PHYADD
AAAAA
AAAAA
REGAD
RRRRR
RRRRR
Description
TA
Z0
10
DATA
IDLE
Z
Z
DDDDDDDDDDDDDDDD
DDDDDDDDDDDDDDDD
Field
PRE
Preamble.
The 10/100 Ethernet transceiver macrocell will accept frames with no preamble. This is
indicated by a 1 in
MR1 status register
, bit 6 (
NO_PA_OK
).
Start of frame.
The start of frame is indicated by a 01 pattern.
Operation code. The operation code for a read transaction is 10. The operation code for a write trans-
action is a 01.
PHY address. The PHY address is 5 bits, allowing for 32 unique addresses. The first PHY address bit
transmitted and received is the MSB of the address. A station management entity that is attached to
multiple PHY entities must have prior knowledge of the appropriate PHY address for each entity.
Register address.
The register address is 5 bits, allowing for 32 unique registers within each PHY.
The first register address bit transmitted and received is the MSB of the address.
Turnaround. The turnaround time is a 2-bit time spacing between the register address field, and the
data field of a frame, to avoid drive contention on
MDIO
during a read transaction. During a write to
the 10/100 Ethernet transceiver macrocell, these bits are driven to 10 by the station. During a read,
the MDIO is not driven during the first bit time and is driven to a 0 by the 10/100 Ethernet transceiver
macrocell during the second bit time.
Data. The data field is 16 bits. The first bit transmitted and received will be bit 15 of the register being
addressed.
Idle condition.
The IDLE condition on
MDIO
is a high-impedance state. All three state drivers will be
disabled and the PHY’s pull-up resistor will pull the
MDIO
line to a logic 1.
ST
OP
PHYADD
REGAD
TA
DATA
IDLE