Specifications

DP83848Q-Q1

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SNLS341C –MARCH 2011–REVISED MARCH 2015

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 DP83848Q-Q1 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 DP83848Q-Q1 (PHY) for a typical register

read access.

For write transactions, the station management entity writes data to the addressed DP83848Q-Q1 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.

Figure 5-2. Typical MDC/MDIO Read Operation

Figure 5-3. Typical MDC/MDIO Write Operation

5.4.3.3 Serial Management Preamble Suppression

The DP83848Q-Q1 supports a Preamble Suppression mode as indicated by a one in bit 6 of the Basic

Mode Status Register (BMSR, address 01h.) If the station management entity (i.e. MAC or other

management controller) determines that all PHYs in the system support Preamble Suppression by

returning a one in this bit, then the station management entity need not generate preamble for each

management transaction.

The DP83848Q-Q1 requires a single initialization sequence of 32 bits of preamble following

hardware/software reset. This requirement is generally met by the mandatory pull-up resistor on MDIO in

conjunction with a continuous MDC, or the management access made to determine whether Preamble

Suppression is supported.

While the DP83848Q-Q1 requires an initial preamble sequence of 32 bits for management initialization, it

does not require a full 32-bit sequence between each subsequent transaction. A minimum of one idle bit

between management transactions is required as specified in the IEEE 802.3u specification.

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