SPRUJ17H March 2022 – October 2024 AM2631 , AM2631-Q1 , AM2632 , AM2632-Q1 , AM2634 , AM2634-Q1
The below Table 7-88 shows the address frame format. Table 7-89 shows read, and write format of the supported Clause 45 frames. Post-increment accesses are not supported.
Pre-amble | Start Delimiter | Operation Code | PHY Address | MMD Number | Turnaround | Address |
---|---|---|---|---|---|---|
MDIO Clause 45 Address Frame Format | ||||||
FFFFFFFFh | 00 | 00 | AAAAA | RRRRR | 10 | AAAA.AAAA.AAAA.AAAA |
Pre-amble | Start Delimiter | Operation Code | PHY Address | MMD Number | Turnaround | Data |
---|---|---|---|---|---|---|
MDIO Clause 45 Read Frame Format | ||||||
FFFFFFFFh | 00 | 11 | AAAAA | RRRRR | Z0 | DDDD.DDDD.DDDD.DDDD |
MDIO Clause 45 Write Frame Format | ||||||
FFFFFFFFh | 00 | 01 | AAAAA | RRRRR | 10 | DDDD.DDDD.DDDD.DDDD |
The default or idle state of the two wire serial interface is a logic one. All tri-state drivers should be disabled and the PHY’s pull-up resistor should pull the MDIO line to a logic one. Prior to initiating any other transaction, the station management entity shall send a preamble sequence of 32 contiguous logic one bits on the MDIO line with 32 corresponding cycles on MDCLK to provide the PHY with a pattern that it can use to establish synchronization. A PHY shall observe a sequence of 32 contiguous logic one bits on MDIO with 32 corresponding MDCLK cycles before it responds to any other transaction. The MDIO_USER_ADDR0_REG/ MDIO_USER_ADDR1_REG registers must be written before a read or write operation is performed to set the address used in the operation. Each read or write operation has a preceeding address frame.
Preamble
The start of a frame is indicated by a preamble, which consists of a sequence of 32 contiguous bits all of which are a “1”. This sequence provides the PHY a pattern to use to establish synchronization. The preamble is required in clause 45 operation.
Start Delimiter
The preamble is followed by the start delimiter which is indicated by a “00” pattern.
Operation Code
The operation code for address is “00". The operation code for a read is “11”, while the operation code for a write is a “01”.
Ethernet PHY Address
The PHY address is 5 bits allowing 32 unique values. The first bit transmitted is the MSB of the PHY address.
MMD Number
The MMD number is 5 bits allowing 32 unique values. The first bit transmitted is the MSB.
Turnaround
An idle bit time during which no device actively drives the MDIO signal shall be inserted between the MMD Number field and the Data field of a read frame in order to avoid contention. During a read frame, the PHY shall drive a zero bit onto MDIO for the first bit time following the idle bit and preceding the Data field. During a write frame, this field shall consist of a one bit followed by a zero bit.
Address
The
address field is 16-bits on address operations. The first bit transmitted is the MSB
of the address word. Each read/write operation initiated has an automatic address
operation initiated first that uses the MDIO_USER_ADDR0_REG[15-0] USER_ADDR0 or
MDIO_USER_ADDR1_REG[15-0] USER_ADDR1 register values as the 16-bit address.
Data
The Data field is 16 bits on read and write operations. The first bit transmitted and received is the MSB of the data word.