ICS1893BKILFT datasheet(42/133 Pages) ICST

42 / 133 page

ICS1893BF, Rev. C, 9/29/05

September, 2005

Chapter 6 Functional Blocks

ICS1893BF Data Sheet - Release

During 10Base-T data reception, a Manchester Decoder translates the serial bit stream obtained from the

Twisted-Pair Receiver (MDI) into an NRZ bit stream. The Manchester Decoder then passes the data to the

MAC Interface in parallel format.

Manchester-encoded signals have the following advantages:

• Every bit period has an encoded clock.

• The split-phase nature of the signal always provides a zero DC level regardless of the data (that is, there

is no baseline wander phenomenon).

The primary disadvantage in using Manchester-encoded signals is that it doubles the data rate, making it

operationally prohibitive for 100-MHz operations.

6.5.2 10Base-T Operation: Clock Synthesis

The ICS1893BF synthesizes the clocks required for synchronizing data transmission. In 10Base-T mode,

the MAC Interface provides a 10M MII (Media Independent Interface):

• 10M MII interface, the ICS1893BF synthesizes a 2.5-MHz clock for nibble-wide transactions

6.5.3 10Base-T Operation: Clock Recovery

The ICS1893BF recovers its receive clock from the Manchester-encoded data stream obtained from its

Twisted-Pair Receiver using a phase-locked loop (PLL). The ICS1893BF then uses this recovered clock for

synchronizing data transmission between itself and the MAC. Receive-clock PLL acquisitions begin with

reception of the MAC Frame Preamble and continue as long as the ICS1893BF is receiving data.

6.5.4 10Base-T Operation: Idle

An ICS1893BF transmits Normal Link Pulses on its MDI in the absence of data. During this time the link is

Idle, and the ICS1893BF periodically transmits link pulses at a rate of one link pulse every 16 ms in

compliance with the ISO/IEC 8802-3 standard. In 10Base-T mode, the ICS1893BF continues transmitting link

pulses even while receiving data. This situation does not generate a Collision Detect signal (COL) because

link pulses indicate an idle state for a link.

6.5.5 10Base-T Operation: Link Monitor

When an ICS1893BF is in 10Base-T mode, its Link Monitor Function observes the data received by the

10Base-T Twisted-Pair Receiver to determine the link status. The results of this continual monitoring are

stored in the Link Status bit. The Station Management entity (STA) can access the Link Status bit in either

the Status Register (bit 1.2) or the QuickPoll Detailed Status Register (bit 17.0).

When the Link Status bit is:

• Zero, either a valid link is not established or the link is momentarily dropped since either the last read of

the Link Status bit or the last reset of the ICS1893BF.

• One, a valid link is established.

The ICS1893BF Link Status bit is a latching low (LL) bit. (For more information on latching high and latching

low bits, see Section 7.1.4.1, “Latching High Bits” and Section 7.1.4.2, “Latching Low Bits”.)

The criteria used by the Link Monitor Function to declare a link either valid or invalid depends upon these

factors: the present state of the link, whether its Smart Squelch function is enabled, and the incoming data.

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