ICS1892 datasheet(49/148 Pages) ICST

49 / 148 page

Chapter 7

Functional Blocks

ICS1892, Rev. D, 2/26/01

February 26, 2001

ICS1892

7.5

Functional Block: 10Base-T Operations

The ICS1892 supports both 10Base-T and 100Base-TX operations. When configured for 10Base-T mode,

the MAC/Repeater Interface can provide either a 10M MII (Media Independent Interface) or a 10M Serial

Interface. The Twisted-Pair Interface is not configurable. ISO/IEC standards specifically define its

operation. (For more information on the Twisted-Pair Interface, see Section 6.6, “Twisted-Pair Interface”.)

There are some important differences between 10Base-T and 100Base-TX operations. The 10Base-T

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

100Base-TX operations (that is, the bandwidth requirements and the line attenuation issues are not as

severe as with 100-MHz operations). Consequently, when the ICS1892 is set for 10Base-T operations, it

uses fewer sublayers 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

The ISO/IEC specification requires the use of a Manchester-encoded signal for 10Base-T operations.

During transmission operations, the ICS1892 acquires data from the MAC/Repeater Interface, in either

4-bit nibbles or as a serial bit stream.

A Manchester Encoder encodes the data before passing it to the Twisted-Pair Transmitter. 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 reception operations, a Manchester Decoder translates the serial bit stream obtained from the

Twisted-Pair Receiver into an NRZ bit stream. The Manchester Decoder subsequently passes the data to

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

The advantages in using Manchester-encoded signals are the following:

• Each bit period has an encoded clock.

• The split-phase nature of the signal always provides a zero DC level regardless of the data.

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 ICS1892 synthesizes the clocks required for synchronizing data transmission. In 10Base-T mode, the

MAC/Repeater Interface can provide either a 10M MII (Media Independent Interface) or a 10M Serial

Interface. When the ICS1892 is configured to support a:

• 10M MII interface, the ICS1892 synthesizes a 2.5-MHz clock for nibble-wide transactions

• 10M Serial Interface to the MAC/repeater, the ICS1892 synthesizes a 10-MHz clock

7.5.3

10Base-T Operation: Clock Recovery

The ICS1892 recovers its receive clock from the data stream obtained from the Twisted-Pair Receiver. It

employs a phase-locked loop (PLL) to recover the clock from this Manchester-encoded data.

Subsequently, the ICS1892 uses this recovered clock for synchronizing the data transmission between

itself and the MAC/repeater. Receive-clock PLL acquisition begins with reception of the MAC Frame

Preamble and continues as long as the ICS1892 is receiving data.

ICS1892 数据表(PDF) 49 Page - Integrated Circuit Systems

ICS1892 数据表(HTML) 49 Page - Integrated Circuit Systems

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

数据表下载