AM79C901AJCT AMD [Advanced Micro Devices], AM79C901AJCT Datasheet - Page 29

• Manufacturer Part Number: AM79C901AJCT
• Description: HomePHY Single-Chip 1/10 Mbps Home Networking PHY
• Manufacturer: AMD [Advanced Micro Devices]

The operation field (OP) follows the start field (ST).
The OP indicates whether the operation is a read or a
write operation. The PHY address (PHYADD) and the
register address (REGADD) that were programmed
follow this. A bus turnaround field (TA) follows the RE-
GADD field. During the read operation, the bus TA
field is used to determine if the PHY is responding
properly to the read request. The final field is the idle
field, and it is required to allow the drivers to turn off.
RX_CLK
TX_CLK
RX_DV
TX_EN
COL
CRS
RXD
TXD
Idle
55
55
55
Figure 14. MII Start of Transmission
D
Preamble
P R E L I M I N A R Y
Am79C901A
The PHYADD field, which is five bits wide, allows 32
unique PHY addresses. The managed PHY layer de-
vice that is connected to a station management entity
via the MII interface has to respond to transactions ad-
dressed to the PHY’s address. A station management
entity attached to multiple PHYs is required to have
prior knowledge of the appropriate PHY address.
For more information, see the IEEE 802.3 specification
and the MII pin descriptions.
55
Data
D
2
22304B-16
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