EE365

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EE365

• More on sequential circuits

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Serial data systems (e.g., TPC)
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Serial data in the phone system (E-1)

• 2.048 Mb/s links between phone switches and
  subscribers
• partitioned into 32 64 Kb/s channels
• Each channel gets a timeslot in a frame where
  it can send 8 bits every 125 ?sec.
• 8000 frames/sec

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Timeslot details
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Parallel-to-serial conversion
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Serial-to-parallel conversion
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Destination timing
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Serial communication on ONE wire

• Serial communication requires three signals
  CLOCK, SYNC, and DATA. Yet only one wire is
  used. How?
• One solution Manchester code.

• Or use a phase-locked loop (analog circuit)to
  extract clock from the data

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Still a couple of problems

• Framing -- SYNC signal
• Solution Use a unique data pattern for SYNC
• PLL clock recovery -- what if too many zeroes are
  transmitted? PLL cant stay in sync.
• Solution Use a code that guarantees a minimum
  number of ones
• Phone system Map 00000000 --gt 00000010 (creating
  slight voice distortion)
• Gigabit Ethernet Uses 8B10B code, solving both
  problems
• Map each byte into 8 bits
• Use only a good subset of 210 code words
• Use another code word for synchronization