ICS1893AF Data Sheet - Release
Chapter 7 Functional Blocks
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.
ICS1893AF, Rev. D 10/26/04
October, 2004
Copyright © 2004, Integrated Circuit Systems, Inc.
All rights reserved.
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