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From: "Rod Pemberton" <do_not_have AT bitfoad DOT cmm>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Performance enhancement for gettimeofday()?
Date: Mon, 15 Jan 2007 16:17:36 -0500
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"Brian Inglis" <Brian DOT Inglis AT SystematicSW DOT Invalid> wrote in message
news:8fulq298bibfkgelg944o93cd0r5jk6kmv AT 4ax DOT com...
> On Sat, 13 Jan 2007 18:18:48 -0500 in comp.os.msdos.djgpp, "Rod
> Pemberton" <do_not_have AT bitfoad DOT cmm> wrote:
>
> >"Brian Inglis" <Brian DOT Inglis AT SystematicSW DOT Invalid> wrote in message
> >news:5t3iq2dlv4hoh2sdf9c4dbot50e6ge28mn AT 4ax DOT com...
> >> On Wed, 10 Jan 2007 13:25:42 -0500 in comp.os.msdos.djgpp, "Rod
> >> Pemberton" <do_not_have AT bitfoad DOT cmm> wrote:
>
> >> ><Gordon DOT Schumacher AT seagate DOT com> wrote in message
> >>
>
>>news:OF77475379 DOT 7BA371D5-ON8725725F DOT 00598107-8725725F DOT 0059B5ED AT seagate DOT com
.
> >..
> >> >> Rod Pemberton wrote on Tue, 9 Jan 2007 at 03:46:03 -0500:
> >> >>
> >> >> # I believe this it the math you'll need:
> >> >> #
> >> >> # 14.318Mhz=4*3.58Mhz=4*(4.5Mhz*455/572)
> >> >> #     (4.5Mhz US TV bandwith/channel, 455 colorburst phase
> >changes/line,
> >> >> 572
> >> >> # total lines/frame including sync)
> >> >> # 14.318Mhz/12=1.93182Mhz
> >> >>
> >> >> Aha, this is the one that's why our numbers don't agree:
> >> >> 14.318MHz divided by 12 is actually 1.193666... MHz.
> >> >>
> >> >
> >> >Sorry, it appears I failed to type a 1 following the decimal.  It's
not
> >> >14.318000MHz, but 14.318181MHz.  You really need to enter
> >> >4*4.5*(10^6)*455/572 to compute the 14.318MHz and work from there.
IIRC
> >> >('twas 25+ years ago), it's 4 times the colorburst as calculated by
the
> >> >original engineer who designed the US color TV standard.  That way you
> >won't
> >> >loose precision.  Of course, a real crystal usually has a tolerance
> >range,
> >> >but that range is usually small compared to the frequency, like +/-
100Hz
> >or
> >> >+/-10KHz.  Of course, you could go to Mouser or another electronic
> >supplier,
> >> >and look for a crystal if you think the range would help.
> >> >
> >> >Like you, I'll use ... for repeating digits.  The 1 and 8 repeat for
> >both.
> >> >I was using more decimals but rounded/truncated.
> >> >
> >> >14.318181818181...  Mhz  / 12 = 1.193181818181... Mhz.
> >> >1.193181818181...Mhz / 65536 = 18.206509676846 Hz
> >>
> >> IIRC crystal frequency 157.5MHz = 9/2*7*5*1E6, /11 colour burst
> >
> >A 157.5Mhz crystal in 1980's?    ROFL!
>
> My assumption was that the frequency is quoted as 157.5/11Mhz various
> places and that commercial broadcast equipment would have generated and
> divided down that reference oscillator (don't really know if it
> could/would have been crystal in the valve/tube era, although WWII army
> radios operated in the 30-40MHz range and came with 72-120 crystals) to
> get an accurate, stable colour burst frequency for transmission.
>

I'll assume you meant: "with 72-120 [Mhz] crystals."

Of course, you didn't state whether they were quartz crystals, or quartz
crystal oscillators...  So, it appears you want an apple vs. oranges
discussion.

Dividing or mixing down an oscillator is a common technique.  But, so is
generating a harmonic or overtone from a lower frequency.  Without
familiarity with broadcast equipment, I'd bet on the later for older
equipment.  Why?  Because dividing down an oscillator frequency is easy with
digital circuitry, but hard without it.  And, mixing down the oscillator
frequency requires intermediate frequencies which have to be generated too.
To me, it's more likely that they attempted to eliminate high frequency (and
high cost) circuitry, which means generating the high frequencies from lower
frequencies: harmonics or overtones.  For new equipment, digital and high
frequencies work well so I see no reason why a video flash DAC circuit
wouldn't use 157.5Mhz.

The point was that 157.5Mhz wasn't used in PC's of the era.  I know that
oscillators well above 1Ghz were available in the '80's, they just weren't
crystal oscillators.

> >In a PC, in the 1980's?    ROFL!  (Where's the Kleenex, I've got to wipe
> >away the tears...)
>
> I'm well aware that TVs and PCs used a 14...MHz crystal.
>
> >Unfortunately, I wasn't actively monitoring the advancement in crystal
> >oscillator frequencies.  However, if you're interested, this link
contains
> >an oscillator frequency timeline:
> >http://www.npcamerica.com/Datasheets/KEYNOTE2.PDF
>
> Timeline actually shows development of *CMOS* ICs for timebase
> generation.
>

No.  The timeline shows the development in frequencies of crystal
oscillators, as I stated.  More specifically, the timeline is for quartz
crystal oscillators using CMOS logic of different voltage levels for the
oscillator, not 100% CMOS (non-crystal) oscillators, as you've  stated.  The
timeline doesn't show the development in frequencies of the quartz crystal
(without integrated oscillator circuitry).

And, yes, it is very possible that the output frequencies weren't limited by
the quartz crystal, but by the ability of the CMOS oscillator circuitry to
function at different voltages and frequencies.  But, then, that applies to
all CMOS IC's.  CMOS circuits can't use frequencies higher than they can
generate.  And, IIRC, CMOS gradually became the dominate logic family of
early CPU's.  So, when one talks about CMOS cpu's with a crystal oscillator,
one shouldn't perceive a large leap of logic to assume the crystal
oscillator is using CMOS also.


1) first quote:

"Our company has been seriously involved in the
CMOS IC crystal oscillator from its birth, and is
producing various clock-signal-generation ICs for
crystal oscillators, which evolved from the quartz clock."

2) second quote:  (Fig. 5. is the timeline)

"In response to the high demand, our company has
developed the CMOS ICs for the oscillator module with
a quartz crystal and an oscillator unified in a package.
This is one of the main products of our company. The
developed and future oscillator products are shown as a
roadmap in Fig.5."


Rod Pemberton