ZHCSAB9E September 2012 – June 2019 DP83848-EP
PRODUCTION DATA.
The serial control interface consists of two pins, Management Data Clock (MDC) and Management Data Input/Output (MDIO). MDC has a maximum clock rate of 25 MHz and no minimum rate. The MDIO line is bi-directional and may be shared by up to 32 devices. The MDIO frame format is shown below in Table 5-4.
MII Management Serial Protocol | <idle><start><op code><device addr><reg addr><turnaround><data><idle> |
---|---|
Read Operation | <idle><01><10><AAAAA><RRRRR><Z0><xxxx xxxx xxxx xxxx><idle> |
Write Operation | <idle><01><01><AAAAA><RRRRR><10><xxxx xxxx xxxx xxxx><idle> |
The MDIO pin requires a pullup resistor (1.5 kΩ) which, during IDLE and turnaround, will pull MDIO high. In order to initialize the MDIO interface, the station management entity sends a sequence of 32 contiguous logic ones on MDIO to provide the DP83848-EP with a sequence that can be used to establish synchronization. This preamble may be generated either by driving MDIO high for 32 consecutive MDC clock cycles, or by simply allowing the MDIO pullup resistor to pull the MDIO pin high during which time 32 MDC clock cycles are provided. In addition 32 MDC clock cycles should be used to re-sync the device if an invalid start, opcode, or turnaround bit is detected.
The DP83848-EP waits until it has received this preamble sequence before responding to any other transaction. Once the DP83848-EP serial management port has been initialized no further preamble sequencing is required until after a power-on/reset, invalid Start, invalid Opcode, or invalid turnaround bit has occurred.
The Start code is indicated by a <01> pattern. This assures the MDIO line transitions from the default idle line state.
Turnaround is defined as an idle bit time inserted between the Register Address field and the Data field. To avoid contention during a read transaction, no device shall actively drive the MDIO signal during the first bit of Turnaround. The addressed DP83848-EP drives the MDIO with a zero for the second bit of turnaround and follows this with the required data. Figure 5-2 shows the timing relationship between MDC and the MDIO as driven/received by the Station (STA) and the DP83848-EP (PHY) for a typical register read access.
For write transactions, the station management entity writes data to the addressed DP83848-EP thus eliminating the requirement for MDIO Turnaround. The Turnaround time is filled by the management entity by inserting <10>. Figure 5-3 shows the timing relationship for a typical MII register write access.