ICS1892 datasheet(57/148 Pages) ICST

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Chapter 7

Functional Blocks

ICS1892, Rev. D, 2/26/01

February 26, 2001

ICS1892

7.6.2.6

Management Frame Turnaround

A valid Management Frame includes a turnaround field (TA), which is a 2-bit time space between the

REGAD field and the Data field. This field requires two bit times and allows the ICS1892 and the STA to

avoid contentions during read transactions. During an operation that is a:

• Read, the ICS1892 remains in the high-impedance state during the first bit time and subsequently drives

the MDIO pin to logic zero for the second bit time.

• Write, the ICS1892 waits while the STA transmits a logic one, followed by a logic zero on the MDIO

signal.

7.6.2.7

Management Frame Data

A valid Management Frame includes a 16-bit Data field for exchanging data between the Management

Registers, and the STA. All Management Registers are 16 bits wide, matching the width of the Data field.

The first Data bit transmitted and received is the most-significant bit of a Management Register, bit X.15.

During a transaction that is a:

• Read, OP is 10b and the ICS1892 obtains the value of the register identified in the REGAD field and

returns the Data to the STA synchronously with the MDC cycles.

• Write, OP is 01b and the ICS1892 stores the value of the Data field in the register identified in the

REGAD field.

If the STA attempts to:

• Read from a non-existent ICS1892 register, the ICS1892 returns logic zero for all bits in the Data field.

• Write to a non-existent ICS1892 register, the ICS1892 isolates the Data field.

7.6.2.8

Idle

MDIO is idle during the time between STA transactions. During this idle time, the ICS1892 disables its

tri-state drivers and the MDIO pin enters a high-impedance state. The ISO/IEC 8802-3 standard requires

that the signal be idle for at least one bit time between management transactions. However, the ICS1892

does not have this limitation as it can support a continual bit stream on its MDIO.

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