ICS1892
TSD
Chapter 7 Functional Blocks
10Base-T/100BIaCseS-TX1I8nt9eg2rated PHYceiver™
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, Rev. D, 2/26/01
February 26, 2001
© 2000-2001, Integrated Circuit Systems, Inc.
All rights reserved.
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IDT™ / ICS™ 10Base-T/100Base-TX Integrated PHYceiver™
ICS1892
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IDT [ INTEGRATED DEVICE TECHNOLOGY ]
