ICS1893AFILF datasheet(47/137 Pages) RENESAS

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Chapter 7

Functional Blocks

ICS1893AF, Rev. D 10/26/04

October, 2004

ICS1893AF Data Sheet - Release

7.5

Functional Block: 10Base-T Operations

When configured for 10Base-T mode, the ICS1893AF MAC/Repeater Interface can be configured to

provide either a 10M MII (Media Independent Interface) or a 10M Serial Interface. The Twisted-Pair

Interface is automatically configured to provide a two-level, Manchester-encoded signal at the voltage

levels specified in the ISO/IEC standard. (For more information on the Twisted-Pair Interface, see Section

6.3, “Twisted-Pair Interface”.)

The 10Base-T and 100Base-TX operations differ as follows. 10Base-T operations are fundamentally

simpler than 100Base-TX operations. The data rate is slower, requiring less encoding than 100Base-TX

operations. In addition, the bandwidth requirements (and therefore the line attenuation issues) are not as

severe as with 100-MHz operations. Consequently, when an ICS1893AF is set for 10Base-T operations, it

requires fewer internal circuits in contrast to 100Base-TX operations. (For an overview of 10Base-T

operations, see Section 5.6, “10Base-T Operations”.).

7.5.1

10Base-T Operation: Manchester Encoder/Decoder

During data transmission the ICS1893AF acquires data from its MAC/Repeater Interface in either 4-bit

nibbles or as a serial bit stream. The ICS1893AF converts this data into a Manchester-encoded signal for

presentation to its MDI, as required by the ISO/IEC specification.

In a Manchester-encoded signal, all logic:

• Ones are:

– Positive during the first half of the bit period

– Negative during the second half of the bit period

• Zeros are:

– Negative during the first half of the bit period

– Positive during the second half of the bit period

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/Repeater Interface in either serial or parallel format, depending on the interface configuration.

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.

7.5.2

10Base-T Operation: Clock Synthesis

The ICS1893AF 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 ICS1893AF synthesizes a 2.5-MHz clock for nibble-wide transactions

7.5.3

10Base-T Operation: Clock Recovery

The ICS1893AF recovers its receive clock from the Manchester-encoded data stream obtained from its

Twisted-Pair Receiver using a phase-locked loop (PLL). The ICS1893AF 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 ICS1893AF is receiving data.

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