ICS1893 Datasheet, PDF (51/152 Pages) Integrated Circuit Systems – 3.3-V 10Base-T/100Base-TX Integrated PHYceiver™

ICS1893 - Release
Chapter 7 Functional Blocks
7.5 Functional Block: 10Base-T Operations
When configured for 10Base-T mode, the ICS1893 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 6.5,
“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 ICS1893 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 ICS1893 acquires data from its MAC/Repeater Interface in either 4-bit nibbles
or as a serial bit stream. The ICS1893 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 ICS1893 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 ICS1893 is configured to support a:
• 10M MII interface, the ICS1893 synthesizes a 2.5-MHz clock for nibble-wide transactions
• 10M Serial Interface to the MAC/repeater, the ICS1893 synthesizes a 10-MHz clock
7.5.3 10Base-T Operation: Clock Recovery
The ICS1893 recovers its receive clock from the Manchester-encoded data stream obtained from its
Twisted-Pair Receiver using a phase-locked loop (PLL). The ICS1893 then uses this recovered clock for
synchronizing data transmission between itself and the MAC/repeater. Receive-clock PLL acquisitions begin
with reception of the MAC Frame Preamble and continue as long as the ICS1893 is receiving data.
ICS1893 Rev C 6/6/00
Copyright © 2000, Integrated Circuit Systems, Inc.
All rights reserved.
June, 2000
51