KS8999_11 MICREL [Micrel Semiconductor], KS8999_11 Datasheet - Page 50

• Manufacturer Part Number: KS8999_11
• Description: Integrated 9-Port 10/100 Switch with PHY and Frame Buffer
• Manufacturer: MICREL [Micrel Semiconductor]

January 2005
Micrel, Inc.
MLT3 Coding
For 100BaseTX operation the NRZI (Non-Return to Zero Invert on ones) signal is line coded as MLT3. The net result
of using MLT3 is to reduce the EMI (Electro Magnetic Interference) of the signal over twisted pair media. In NRZI
coding, the level changes from high to low or low to high for every “1” bit. For a “0” bit there is no transition. MLT3 line
coding transitions through three distinct levels. For every transition of the NRZI signal the MLT3 signal either
increments or decrements depending on the current state of the signal. For instance if the MLT3 level is at its lowest
point the next two NRZI transitions will change the MLT3 signal initially to the middle level followed by the highest
level (second NRZI transition). On the next NRZI change, the MLT3 level will decrease to the middle level. On the
following transition of the NRZI signal the MLT3 level will move to the lowest level where the cycle repeats. The
diagram below describes the level changes. Note that in the actual 100BaseTX circuit there is a scrambling circuit
and that scrambling is not shown in this diagram.
MAC Frame
The MAC (Media Access Control) fields are described in the table below.
Field
Preamble/SFD
DA
SA
Length
Protocol/Data
Frame CRC
ESD
Idle
Octect Length
46 to 1500
Variable
8
6
6
2
4
1
Description
Preamble and Start of Frame Delimiter
48-bit Destination MAC Address
48-bit Source MAC Address
Frame Length
Higher Layer Protocol and Frame Data
32-bit Cyclical Redundancy Check
End of Stream Delimiter
Inter Frame Idles
Figure 20. MLT3 Coding
Table 14. MAC Frame
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