sync signal generator
BH...@psuvm.bitnet
video sync signal would be. Preferably it would be best crystal locked. I
have already tried the sync out from a commercial RCA video camera. It didn't
work well enough. I was able to borrow a digital time base corrector and
the sync sigal for it worked. The specific application is an Ardent Workstatio
computer. The RS-170(NTSC) output from it requires that you put in a external
sync signal.
Forrest Cook
>Does anybody know hwat the loewst cost device that would generate a 60Hz
>video sync signal would be.
>The specific application is an Ardent Workstation computer.
>The RS-170(NTSC) output from it requires that you put in a external
>sync signal.
RS-170 and NTSC are very different color signals, RS-170 uses separate
R G and B lines and NTSC puts it all on the same signal.
In 3 wire RS-170 setups, the sync signals (negative pulses) are often
sent along the same line as the green video signal (positive waveform)
during retrace. A fairly simple comparator circuit set to trigger on the
Vsync level should work as a Vertical Sync Separator. It is best to look
up some kind of RS-170 spec (preferably from Ardent in your case) to get
the exact specs on the signal.
^ ^ Forrest Cook - Beware of programmers who carry screwdrivers - LB
/|\ /|\ co...@stout.ucar.edu (The preceeding was all my OPINION)
/|\ /|\ {husc6|rutgers|ames|gatech}!ncar!stout!cook
/|\ /|\ {uunet|ucbvax|allegra|cbosgd}!nbires!ncar!stout!cook
Tom Leach
>In article <89216.120136BHB3@PSUVM> BH...@PSUVM.BITNET writes:
>...
>>The specific application is an Ardent Workstation computer.
>>The RS-170(NTSC) output from it requires that you put in a external
> ????????????
>
>R G and B lines and NTSC puts it all on the same signal.
Nope, I think that you got that switched around. RS-170A refers to an
NTSC-encoded composite signal. You can use and encoder to take
component RGB signals and convert them into a RS-170A signal, but the
RS-170 is definately an NTSC signal. (Feb 89 iss of AV Video has a
short piece on RS-170A and RGB in the Q&A column)
Tom Leach
Internet:le...@OCE.ORST.EDU UUCP:{tektronix, hp-pcd}!orstcs!leach
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Middle-of-the-road, man, it stanks. Let's run over Lionel Richie with a tank.
>>>Disclaim: It's me, not OCE.<<< B. Catt, Deathtongue. (c 1986)
Charles A. Poynton
> video sync signal would be.
To cut a long story short, I suggest a VIDI/O BOX (TM) from Truevision,
Inc. 800-858-8783, list $995.
Certainly crystal stability will be required for your application
(therefore you need 59.94 Hz field rate, not 60 Hz). Just horizontal and
vertical 4 V 'sync' might work, it depends on the device being fed, but I
suggest (and the VIDI/O BOX provides) 1 V "black burst" which includes
colour burst and pedestal, and is in fact exactly a legal black video
signal.
All respectible (broadcast or industrial) video equipment will free-run
and generate legal timing in the absence of reference video in, this may
or may not be true of your workstation. I suspect that your workstation
requires reference sync only so that an external sync generator can
generate subcarrier locked to the sync. This is to allow you to
externally encode a coherent NTSC colour signal, that is, a signal in
which the colour subcarrier is phase-locked to the horizontal sync. The
VIDI/O BOX includes an encoder.
I suspect that your workstation outputs is colloquially called "RGB with
RS-170-A timing" and not what you refer to as "RS-170(NTSC)"; the
distinction is the subject of a following article.
C.
-----
Charles A. Poynton Sun Microsystems Inc.
<poy...@sun.com> 2550 Garcia Avenue, MS 8-04
415-336-7846 Mountain View, CA 94043
"Japan has no laws against damage to its flag, but it has strict laws
forbidding the burning of foreign flags lest this give offense to the
country in question." -- The Economist, July 1, 1989, p. 19.
-----
Charles A. Poynton
> RS-170 and NTSC are very different color signals, RS-170 uses separate
> R G and B lines and NTSC puts it all on the same signal.
RS-170 refers to 525-line, 60.00 Hz field rate MONOCHROME.
> RS-170A refers to an NTSC-encoded composite signal.
True.
> RS-170 is definately an NTSC signal.
RS-170 is definitely MONOCHROME.
Pardon my obsession with detail, but video is confusing enough without
cascaded nomenclature error and ambiguity. Here are the facts.
RS-170, without "A", refers to 525-line, 60 Hz field rate, monochrome
video. The horizontal line rate in monochrome systems used to be exactly
15.750 kHz (within some tolerance). EIA RS-170 (now properly denoted
"EIA-170") was written by the first NTSC, in about 1943.
Upon the introduction of colour by the second NTSC in 1953, the FCC forced
the horizontal line rate of broadcast television to be reduced by
precisely 0.1%. [It was necessary to change the ratio of the 4.5 MHz
sound subcarrier to the horizontal line rate to reduce the visibility of
certain sound/picture interference products, and the anecdote goes that
the FCC may not have understood picture very well, but they understood FM
modulated sound, and THAT was going to stay put, so the raster timing was
changed and we have been stuck with dropframe video ever since. This is
all now seen to be pretty silly since the sound is FM, so it rarely rests
at exactly 4.5 MHz anyway!] This is how we got our current horizontal
line rate of nominally 15.734 kHz and a field rate of 59.94 Hz, and even
monochrome systems now run at these rates, making RS-170 quite obsolete.
The FCC adopted the NTSC broadcast spec in 1953, and the EIA worked for
years and years on standardizing a companion studio signal standard which
was to be revision "A" of RS-170. This work NEVER achieved the agreement
necessary to become adopted as a standard, so on November 8, 1977, the EIA
published, get this, "EIA Industrial Electronics Tentative Standard
No. 1". This standard, and the associated classic 11-by-17 foldout timing
diagram, is what I refer to as "EIA No. 1" and what is colloquially and
incorrectly referred to as RS-170-A. [Proper nomenclature would now be
along the lines of "EIA-232-C" anyway, if it were a standard.] In
the light of the failure of EIA to conclude this work, the SMPTE are now
working to standardize a 525/59.94 NTSC studio signal standard, roughly
thirty five years later. History is poised to repeat itself in the
development of U.S. HDTV standards.
Conclusions:
NTSC refers to composite (encoded) colour video.
"EIA No. 1" is the standard which defines an NTSC colour signal.
"RS-170-A" doesn't exist, but implies EIA No. 1 and therefore NTSC.
"RS-170-A RGB" is a self-cancelling term.
"RS-170 RGB" indicates 60.00 Hz field rate; absolutely nobody uses this.
Most computer equipment avoids the complexity of NTSC encoding, but
generates RGB signals with the same timing. Until SMPTE publishes a
standard, such equipment should be described as "RGB with EIA No. 1
timing".
C.
-----
Charles A. Poynton Sun Microsystems Inc.
<poy...@sun.com> 2550 Garcia Avenue, MS 8-04
415-336-7846 Mountain View, CA 94043
"Solutions, not slogans." -- slogan from Analog Devices, Inc., circa 1985.
-----
Mark Robert Thorson
of a composite sync signal, you can use the National Semiconductor MM5320 TV
camera sync generator chip (if they still make it). It outputs a composite sync
signal. It can be sync'ed up to an external signal. Ferranti also makes
a composite sync generator, but I don't recall if it can be sync'ed up to
an external signal. I believe it can. The National chip is much cheaper,
unless you count the cost of a -12V power supply. (Ferranti is 5V only.)
I haven't heard of National re-casting the 5320 in n-MOS. It would be
a sensible thing to do. I've worked with the p-MOS version. Here are
some tips:
1) The outputs are TTL compatible, but they're not TTL. They pretty much
swing between near +5 and near -12. This is important to know if you are
designing a resistor summer to mix the sync with the video.
2) This chip really surges on the power consumption at certain points in
its cycle. You need a good-size decoupling capacitor on the -12 supply
right near the chip. I used 22 uF.
3) This chip runs hot. Take appropriate precautions.
THe last time I bought chips, it was from Advanced Computer Products somewhere
near LA. Half the chips didn't work. They ignored my requests for a refund.
I do not recommend doing business with them.
Isaac S Wingfield
remember something that's puzzled me for a long time:
*exactly* what are the "equalizing pulses" for?
No guesses, please; I've made and been offered lots of those.
If you *know*, please enlighten me.
Isaac i...@cup.portal.com
Jim Cathey
>R G and B lines and NTSC puts it all on the same signal.
RS-170 is monochrome. Isn't the 3-wire RGB RS-170-like video spec RS-343?
I can't remember anymore.
+----------------+
! II CCCCCC ! Jim Cathey
! II SSSSCC ! ISC-Bunker Ramo
! II CC ! TAF-C8; Spokane, WA 99220
! IISSSS CC ! UUCP: uunet!iscuva!jimc (ji...@iscuva.iscs.com)
! II CCCCCC ! (509) 927-5757
+----------------+
"With excitement like this, who is needing enemas?"
Rob Warnock
+---------------
| I'm not really sure I understand your question, but if you want a source
| of a composite sync signal, you can use the National Semiconductor MM5320 TV
| camera sync generator chip (if they still make it). It outputs a
| composite sync signal. It can be sync'ed up to an external signal.
Ah, yezzz... used it once in a project I was doing...
Jameco (a local/mail_order distributor) still carries it; cost is about
$12 each. But it's listed as a "closeout item, will not be reordered".
(But it's been listed that way for over a year now...)
+---------------
| ... The National chip is much cheaper,
| unless you count the cost of a -12V power supply.
| ...some tips:
| 1) The outputs are TTL compatible, but they're not TTL. They pretty much
| swing between near +5 and near -12. This is important to know if you are
| designing a resistor summer to mix the sync with the video.
+---------------
Or if you want to feed something other than TTL, like CMOS. The current that's
sourced from the -12 supply can blow CMOS inputs (or even blow the whole chip
by causing the CMOS to go into "latch-up"), so use a "real" TTL or LS-TTL
chip as a buffer first. The National chip's outputs are actually *designed*
to use the input undershoot diodes of the following TTL input as a clamp on
the output voltage. (Ugh!)
+---------------
| 2) This chip really surges on the power consumption at certain points in
| its cycle. You need a good-size decoupling capacitor on the -12 supply
| right near the chip. I used 22 uF.
| 3) This chip runs hot. Take appropriate precautions.
+---------------
Ottherwise, it works o.k., I guess...
But for just those reasons, plus the uncertainty about future availability,
I gave up using it and built a PROM/counter-based circuit instead. A naive
version would use 455 x 525 locations (clocked at Color-Burst x 2), but you
can do what the National chip does and clock at (CB * 4) / 7 = 2.045454286 Mhz
which gives 130 clocks per H line, or 130 x 525 = 68250 locations in the PROM.
[Note that "CB*4" is supplied on the bus of most IBM PC clones.]
Since most EPROMs are 8 bits wide, you can use some of the extra bits that
you wouldn't need for outputs to do some run-length compression, which lets
you pack the pattern into a 4Kx8 EPROM (2732 or equiv). [A slightly simpler
counter circuit uses more ROM but still gets it into a single 2764 EPROM,
at about the same price. You also get an extra usable output, which I use
for a "test pattern".]
Using a 29C64 EPROM and 74HCTxxx counters, the power drain is pretty low.
The total parts cost is *less* than the National chip, though the board
area is greater. Besides, you get to completely choose the outputs.
The outputs I needed were NTSC composite sync, NTSC composite blanking,
start_of_line (similar to H_sync, but keyed at the edge of blanking),
start_of_field (similar to V_sync, but keys on at line 22), and "test_pattern".
(The other three bits go back to the first counter section and control
how many clocks to repeat each output pattern.) If you feed the composite
sync, blanking, and test pattern outputs to a simple resistive adder, you
get an analog output monochrome composite-video test pattern.
Using a bigger PROM, you could use an address bit to select between several
patterns stored in the ROM, for example, between NTSC and PAL.
More details if anybody really needs them...
Rob Warnock
Systems Architecture Consultant
UUCP: {amdcad,fortune,sun}!redwood!rpw3
DDD: (415)572-2607
USPS: 627 26th Ave, San Mateo, CA 94403
Vidiot
<
<Otherwise, it [MM5320] works o.k., I guess...
Yep, the part works just fine. I use it to drive the sync inputs on the
3/4" Umatic decks that I use for editing (through a TTL buffer). I also
have a sync separator part that I use to set off a one-shot to resync the
sync generator every frame. The one shot is used because the timing of the
signals available do not exactly match what the generator needs, but since
one of them is early enough, I put it through a one-shot.
The problem with the 3/4" Sony decks (older ones) is that when the input
video is used for sync, a very minor glitch will cause the recorder to
lose gen-lock. It is worse when editing and the source tape is used as the
sync source. So, by feeding external sync into both decks, there isn't a
sync separator problem in the 3/4" deck. I looked at the internals of the
3/4" and noticed that the composite video signal used as sync was about
1/5th of the size of external TTL sync. This extra level internally provided
enough to keep glitches from screwing things up.
I use the sync separator to take in video signals from the TV and provide
re-sync for the sync generator. This keeps minor glitches from screwing up
the 3/4" deck when recording off-the-air stuff. Also, the one-shot is such
that it finishes a short while before the next frame starts, keeping random
glitches between frames was causing random re-syncs. Of course, massive
changes in original sync timing will still cause glitches. If only I had
a frame-store unit :-)
--
harvard\ att!nicmad\
Vidiot ucbvax!uwvax..........!astroatc!brown
rutgers/ decvax!nicmad/
ARPA/INTERNET: brown%astroa...@spool.cs.wisc.edu
Steve Ludtke
If you just need a simple sync signal, and you have some sort of video source,
the LM1881 is an excellent choice. It's pretty new; it provides composite
sync, vertical sync, burst/back porch, and odd/even frame output, all in a
8 pin package. It takes any NTSC (might deal with PAL too) video signal as
an input, and requires only 3 external components and a +5 thru +12 volt
power supply. I've tried it with a number of video sources for genlocks,
video decipering, etc ... and it's worked quite well. Even better, they
only cost $4-6 each. I've seen a number of different scemes for accomplishing
the same thing as this single chip. It usually involved several IC's and
numerous resistors and cap's, and was usually less reliable than this. In
any case, it's made by national, and might be worth looking into.
---------------------------------------------------------------------------
Steve Ludtke
ste...@tybalt.caltech.edu ..!cit-vax!tybalt.caltech.edu!stevel
stevel@citiago (Bitnet) OBS949 (Amer PPl lnk)
72335,1537 (Compuserve) XJM16487 (Genie)
Charles A. Poynton
> *Exactly* what are the "equalizing pulses" for?
>
> No guesses, please; If you *know*, please enlighten me.
Indeed as Bob Myers suggests [no References: line, otherwise I'd quote],
the equalizing pulses have to do with interlace. Since you ask for an
*exact* explanation, I'll explain in detail.
The first thing you need to know is that if you attempt to just jam
composite video down to -40 IEEE solidly for three lines of vertical sync,
the horizontal oscillator will freerun for those lines, and it will take a
few (or many) lines to get synchronized back to the incoming video when H
syncs resume. This used to be known as "EIAJ" or "industrial" sync, and
can lead to 'flag waving' at the top of the picture, in the worst case.
So it is necessary to 'serrate' the vertical pulse, in order to provide H
sync information during vertical.
The next thing you need to know is that in an interlaced system, the first
vertical (broad) sync pulse in one field needs to be coincident with an H
sync, and the first vertical pulse in the other field needs to occur half
way between two H syncs. If you don't kick V very very nearly half way
through a line, at the top of the even field, then the lines 'pair', that
is bunch up together leaving black bar in between, and this causes an
objectionable picture im-pair-ment (pardon me, it's getting late).
Now, take yourself back to 1941. You've got vacuum tubes, but not very
many of them, and you've got Rs and Cs. To separate the vertical and
horizontal components of sync, you use an R and a C in each leg, as cheapo
HP and LP filters. Basically the V filter is an integrator that ramps up
while composite video is below -20 IEEE (whoops, IRE, this is 1941), and
leaks back down slowly when it's above. During the picture lines, the
leak rate is faster than the little pumps it gets from the little 4.7 us H
syncs, and the integrator output sits down at some saturation level, but
when broad pulses start arriving, with about 54 us of time below -20 IRE
per line, it ramps up considerably. There's a slicer that kicks the V
flyback when the integrator passes a threshold. The trouble is, because
the filter pair is so cheap, a little H contribution gets into the
separated V. The amount and timing of that extra energy depends on which
field you're in, and if there were just full-width H syncs and a line-wide
V sync, that would induce line pairing.
So equalization pulses were introduced, so that if you look at any V sync
event, a string of six broad pulses, the immediate neighborhood before and
after comprises exactly the same pattern: six 2.3 us "equalizing" pulses
at twice H rate, and six 27 us broad pulses at twice H rate. That makes
one field look "equal" to the other in terms of H sync contribution to the
V integrator; in other words, a thresholded V sync event can't tell which
field it came from. This arrangement prevents line pairing.
The resulting equalization/broad pulse pattern is what produces the
sideways-"T" pattern that you see if you turn up the brightness and roll
down vertical hold (if anybody's still GOT a vertical hold control).
Now of course, with decent analog and digital ICs, all of this is quite
redundant. Work done in the Soviet Union a few years ago concluded that
we could now safely do away with all but a single pre-equalizer even for
the current aging population of 525/59.94 and 625/50 receivers. HDTV will
retain twice-line-rate broad pulses, but have a single pre-equalizing
pulse in one field and a single post-equalizing pulse in the other.
By the way, Bob, I insist on "EIA No. 1" as part of my campaign to
embarrass the EIA and the SMPTE into adopting a standard.
C.
-----
Charles A. Poynton Sun Microsystems Inc.
<poy...@sun.com> 2550 Garcia Avenue, MS 8-04
415-336-7846 Mountain View, CA 94043
"Japan has no laws against damage to its flag, but it has strict laws
Stephen King
>If you just need a simple sync signal, and you have some sort of video source,
>I've tried it with a number of video sources for genlocks,
>video decipering, etc ... and it's worked quite well. Even better, they
Another interesting component is (was) the Motorola MC1378 video overlay
synchronizer. Put NTSC in and get everything out, including phase locked
10xSc clock (35.8 Mhz). External circuitry has to feed H sync back to the
chip - we accomplished that with one PAL. The thing also had RGB and
overlay enable inputs. Anyway, what we worked with was a pre-production
sample (labelled XC1378), and I haven't heard whether or not these things
ever made it to full production. Anyone got more info?
--
Se non e` vero, e` ben trovato
...{utzoo|mnetor}!dciem!dretor!king ki...@dretor.dciem.dnd.ca
Mark Robert Thorson
your sync signals) you may need a reference for the TV sync signal itself.
I once got an excellent booklet on the timing of standard TV signals for
free from the local Tektronix representative. I believe the book was called
TELEVISION BROADCAST MEASUREMENTS. It is a book intended for the engineer
at a TV station, and tells what measurements you need to take, and how
to take them, in order to comply with FCC standards.