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From: Tim Wescott on 8 Aug 2010 13:18
On 08/06/2010 03:42 AM, Daku wrote:
> Thanks to all for your feedback. I had thought
> about the baud rate idea that Tim elaborated
> on, but the context in which I asked this question
> was Ethernet bits going from the MAC layer
> to the PHY layer at say 1 Gb/s or more (for the
> newer standards).
>
OOps -- http://en.wikipedia.org/wiki/Ethernet_over_twisted_pair has a
link to IEEE 802.3.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html
From: Grant on 8 Aug 2010 16:49
On Sun, 8 Aug 2010 09:00:08 -0700 (PDT), Daku <dakupoto(a)gmail.com> wrote:

>Bit values may be inferred from the specified voltage levels,
>as in stabdard CMOS - analogous to a timing diagram.

And data framing? Bit and byte/word separation? A square wave conveys
no information until you agree on how to interpret it, frequency? So
you need to modulate the pulse train in some fashion, agreed beforehand
at both ends before you can convey information.

Basic information theory: sender and receiver must first agree on a
dictionary :)

Grant.
>
>On Aug 8, 9:29 am, Grant <o...(a)grrr.id.au> wrote:
>>
>> depends how you do the data framing too, how do you tell if a bit is a
>> one or zero?
>>
>> Grant.
From: Grant on 8 Aug 2010 16:55
On Sun, 08 Aug 2010 10:17:50 -0700, Tim Wescott <tim(a)seemywebsite.com> wrote:

>On 08/06/2010 03:42 AM, Daku wrote:
>(top posting fixed)
>> On Aug 6, 3:25 am, "k...(a)att.bizzzzzzzzzzzz"<k...(a)att.bizzzzzzzzzzzz>
>> wrote:
>>> On Fri, 06 Aug 2010 06:49:33 +1000, Grant<o...(a)grrr.id.au> wrote:
>>>> On Thu, 5 Aug 2010 16:19:00 -0400, "Tom Biasi"<tombi...(a)optonline.net> wrote:
>>>
>>>>> "Daku"<dakup...(a)gmail.com> wrote in message
>>>>> news:1f08b0d9-9d6a-4cf3-93cc-19803e81b278(a)y32g2000prc.googlegroups.com...
>>>>>> I understand that they are different domains (Hz - analog and bits/sec
>>>>>> - digital), how would one
>>>>>> convert e.g., 1Gbit/s to corresponding Hertz
>>>>>> frequency ?
>>>
>>>>> Hi,
>>>>> Tim is quite knowledgeable on these subjects and gave some usefull info but
>>>>> maybe your question is not quite so deep.
>>>>> Hertz is used to describe cycles/second (cycles per second). If you allow it
>>>>> to mean events per second then a bit can be an event.
>>>>> So 1Gb/sec is 10^9bits / sec or 1 Ghz.
>>>>> This is for mental clarity and the actual units may vary.
>>>
>>>> Yes, Tim touches on the old baud rate (symbol rate) vs frequency that
>>>> you're suggesting as the simple answer.
>>>
>>>> Both are not incorrect (double negative only to show grey area).
>>>
>>>> For example 100Mbps network link bangs four symbols on each of 1/25MHz
>>>> to get the speed, and Gbps copper network links don't run at 1GHz, they
>>>> run slower speed, using a couple pairs in each direction.
>>>
>>>> So, in this case, context matters.
>>>
>>>> Where I said symbols, Tim said constellation, Tim is more accurate :)
>>>
>>> Not really. Symbols are the stars in a constellation of stars. The symbol is
>>> the basic unit of information transferred. A constellation is a
>>> representation of the possible physical values (voltage, frequency, phase,
>>> whatever).
>>>
>>> A little more specifically, a symbol may be a specific value in the
>>> constellation or a transition from the current point to another.
>>
> > Thanks to all for your feedback. I had thought
> > about the baud rate idea that Tim elaborated
> > on, but the context in which I asked this question
> > was Ethernet bits going from the MAC layer
> > to the PHY layer at say 1 Gb/s or more (for the
> > newer standards).
>
>GB Ethernet uses 5-level signaling on four pairs of wires. I can't find
>a reference that gives the symbol rate; without forward error correction
>(FEC) it could be as low as 110MBaud. I don't believe this at all-- I'm
>sure there's at least some coding to keep the average voltage at 0 for
>transformer coupling, for error detection, and maybe even for error
>correction.

Rather magical, part of the training sequence (on copper) determines
cable length ;)

Grant.
>
>But surfing on Wikipedia for a few moments didn't tell me -- you'll have
>to dig up the appropriate standard and take a look for yourself!
>
>http://en.wikipedia.org/wiki/Ethernet_over_twisted_pair has a
>discussion, and a link to IEEE 803.
From: Daku on 9 Aug 2010 02:51
On Aug 8, 9:27 pm, Gareth <m...(a)privacy.net> wrote:
> What exactly are you trying to do here? a bit of background may help
> answer your question. E.g. are you trying to send data down a cable? if
> so will it be synchronous or asynchronous? Is it just one way
> communication between two devices?
I am creating Verilog models of high-speed Ethernet protocols (e.g.,
>= 1Gbit/sec). All data movement is in between the sub-circuits of
an integrated circuit. However, some of the IEEE specification
documents that I have read do not mention any of the coding
schemes etc.
>
> Gareth.
>
> PS top posting, that's posting your reply above the relevant text, can
> make threads difficult to follow. it is usually clearer to put your
> reply below the relevant text in the post you are replying to.

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