if it does then when will a clock be useful in decoding bipolar signals

'I was thinking' it just see if it detects a -voltage & a +voltage and do "save " the bits accordingly

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1 Answer 1


All serial signals require some kind of clock - either in a separate channel or (more commonly) embedded into the signal.

The basic problem is that the receiver loses track of the transmitter's symbol stepping when there are too many identical symbols in sequence (=the line doesn't change at all for a while). Whether you use electrical, single-ended, differential, optical or wireless signaling doesn't matter.

E.g. when the sender transmits ten zeros 0000000000, the receiver may read that back as nine zeros or eleven zeros. The actual number of bits after which a resynchronization is required varies with PLL technology, but it's finite.

A simple COM link commonly sends a fixed 0 in front of (start bit) and a fixed 1 after each user byte (stop bit).

Early Ethernet uses Manchester code which runs a clock at twice the data rate and modulates it with the user data. Fast and Gigabit Ethernet use 4b/5b and 8b/10b respectively which ensure resynchronization after 5 bits at most. 10G Ethernet uses 64b/66b, forcing resync after 66 bits.

  • is it possible that it just see if it goes from0 to 1v and it write bit 1 and 0to -1 and write bit0 so no matter what time lenght and bit period ,isn't that sufficient @Zac67 Jul 24, 2021 at 10:53
  • You need to be able to track any number of same 0 or 1 bits - not possible without any clock.
    – Zac67
    Jul 24, 2021 at 11:05
  • but the 'tracking 'is in the pc with some electronics ,;just it's going to account bit 1 for a positive voltage and bit 0 for a negative even if they are little distance a part ,and to end signal voltage 0 ,in ethernet wires ,10 base it's like that but they maybe talk about clock idon't see the use youtu.be/i8CmibhvZ0c?t=363 "i preset the time in video it shows" Jul 24, 2021 at 11:29
  • Yes, the some electronics requires some clocking to distinguish 10 or 11 zero bits (or one bits). More sophisticated electronics requires less clocking (100 or 101 one bits?) but still. 10BASE-T uses Manchester code for clock recovery with two levels per user bit - -+ for 1 or +- for 0. Simple but wasteful.
    – Zac67
    Jul 24, 2021 at 11:45
  • so a clock is used whitout "need" ; but is it technically what i said possible,; Jul 24, 2021 at 13:53

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