1 EE365 More on sequential circuits

2 Serial data systems (e.g., TPC)

3 Serial data in the phone system (E-1) Mb/s links between phone switches and subscribers –partitioned into Kb/s channels Each channel gets a timeslot in a “frame” where it can send 8 bits every 125  sec. –8000 frames/sec

4 Timeslot details count = 255

5 Parallel-to-serial conversion  256 LSBs are bit number Assert shift-register LOAD input during bit 7 Timeslot number can be decoded and used to select source of parallel data Serial data to destination count = 255

6 Serial-to- parallel conversion Synchronize destination’s counter to source’s Shift in serial data Detect that a complete byte has been received Holding register for complete byte Note: loads 0…0

7 Destination timing Serial-in, parallel-out shift register outputs Holding-register outputs Grab complete byte when available

8 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:

9 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 can’t stay in sync. –Solution: Use a code that guarantees a minimum number of ones –Phone system: Map > (creating slight voice distortion) Gigabit Ethernet: Uses 8B10B code, solving both problems –Map each byte into 8 bits –Use only a “good” subset of 2 10 code words –Use another code word for synchronization