Region 0 DVDs
 

On Thu, 28 Feb 2008 12:35:19 +0000, Ian Jackson
wrote:

In message , John Evans
writes
On Thu, 28 Feb 2008 10:36:19 -0000, Roderick Stewart
wrote:

crystal oscillator would respond much too slowly, so in fact it would make
matters worse. Mostly the oscillators are just based on RC charging circuits
and free-run about 10%-20% slow unless triggered.

Rod.



Oscillators in TVs aren't triggered. If they were the timebase would
stop in the abscence of a signal. The are synchronised and run slow in
the abscence of a sync signal.

Which explains why a set with a 50Hz field will usually lock to a 60Hz
signal, but not vice versa.

But I think you are splitting hairs over Rod's use of 'triggered'. His
explanation is absolutely 100% correct.


I'm thinking of anyone following this thread who wants to understand
how things work, or who wants to diagnose faults. In which case the
correct terminology is important.

I agree that a timebase can be "triggered" into synchronisation by a
pulse, but there is a difference between a triggered time base, that
requires a pulse to operate, and a free running one that is
synchronised by a pulse.

Region 0 DVDs
 

In article , John Evans
wrote:
I'm thinking of anyone following this thread who wants to understand
how things work, or who wants to diagnose faults. In which case the
correct terminology is important.
*
I agree that a timebase can be "triggered" into synchronisation by a
pulse, but there is a difference between a triggered time base, that
requires a pulse to operate, and a free running one that is
synchronised by a pulse.

I'm using the terminology they used at Wood Norton, and which I've seen
used in magazines like Wireless World. My understanding is that a
trigger pulse is a pulse that triggers an event of some sort, in the
case of a TV field timebase the discharge of the timing capacitor. In
the absence of the external trigger pulse the capacitor would
eventually be discharged by other means, but I don't see that this
makes any difference, as the external trigger pulse, when it is
present, does in fact trigger it.

If a trigger pulse triggers an event, then there's an implication that
in the absence of the pulse, something will fail to happen - which is
exactly how it is. The thing that fails to happen need not be the
continuous running of an oscillator, but just its return to some
starting condition at a particular time.

I don't know how it is in all branches of electronics, but in
television, a pulse that is required to produce an output from a
subsequent circuit (rather than simply to control its timing) would be
called a drive pulse. One of the pulses from the old style sync
generators was called "Line Drive", and at least the earliest cameras
required it for the line "oscillator" to produce an output. I've even
encountered computer monitors like this, i.e. when there is no line
drive signal from the computer, horizontal scanning in the monitor
simply stops, and there is no EHT either because the same circuit does
both.

Rod.

Region 0 DVDs
 

In message , Jim Lesurf
writes
In article
,
wrote:
On 27 Feb, 15:32, "David" wrote:


There are two discs, both "Region 0". One will play fine in my
Panasonic DMR-E55, the other will not. When the blue DVD logo appears,
it has a message superimposed on it to the effect that "You cannot play
discs from this region". This disc plays fine in my PC.

The Panasonic manual states that "You cannot play DVD-Video if their
region number does not include "2" or "All". The DVD-Video region
number indicates the disc conforms to a standard. You cannot play discs
that do not have a region number". I've been in touch with the supplier
of the discs (I'm in the UK, the discs are from the USA) and he says
that both discs were manufactured and encoded identically.

Well, if the non-playing disc isn't a faulty one, then your experiment
apparently refutes his theory. :-)

Contact them again and ask which is more likely, that the disc is faulty
and should be replaced, or that his theory is incorrect. If the former,
then a replacement or refund would be due, I assume.

The only difference I can find is that the one that doesn't play has
24bit PCM. I suppose it's possible that the one that DOES play has
flags 1-6 set, and the other has no flags set - both therefore Region 0,
but only one playable in my picky and hitherto unimpeachable Panasonic
player. What I need is a tool that will read the underlying flags of
the Region code.

When a disc is marginal or faulty in some way it can be hard to predict in
advance which players/drives will play it OK, and which won't.

Slainte,

Jim

If it only the one DVD which is giving you the problem, have you tried
to play it in your computer? If you don't have a program installed which
will play DVDs - or you do have one, but which will only play Region 2
(unless you change the setting for the DVD drive - and you won't want to
do that) - install something like VLC Media Player, which ignores DVD
regions. If you can get it to play OK, why not copy it to another disk?
--
Ian

Region 0 DVDs
 

If a trigger pulse triggers an event, then there's an implication that
in the absence of the pulse, something will fail to happen - which is
exactly how it is. The thing that fails to happen need not be the
continuous running of an oscillator, but just its return to some
starting condition at a particular time.

I don't know how it is in all branches of electronics, but in
television, a pulse that is required to produce an output from a
subsequent circuit (rather than simply to control its timing) would be
called a drive pulse. One of the pulses from the old style sync
generators was called "Line Drive", and at least the earliest cameras
required it for the line "oscillator" to produce an output. I've even
encountered computer monitors like this, i.e. when there is no line
drive signal from the computer, horizontal scanning in the monitor
simply stops, and there is no EHT either because the same circuit does
both.

Rod.



There is a fundamental difference between a triggered timebase and a
synchronised one. In a triggerd timebase the pulse initiates the scan
and in a synchronised one it initiates the flyback.

The latter can be seen on the video waveform where the black period
after the video information ,and prior to the sync pulse, is the
"Front Porch" and the one after it, and before the video, is the "Back
Porch". The flyback takes place after the front edge of the pulse and
before the end of the back porch.

Both can be seen on an oscilloscope where the timebase can be either
Triggered/Freerunning/One (or single) shot. (Some times the triggered
is made to free run at a low scan rate so that the spot can be seen).
The trigger level starts the scan. A one shot is a triggerd time base
that is held off until an event occurs - sometimes just the user
pushing a button.

I know that it can be said that the sync pulse triggers ( better -
initiates) the flyback and that a triggerd timebase is synchronised
but that is not how they are defined.

Region 0 DVDs
 

In article ,
John Evans wrote:

If a trigger pulse triggers an event, then there's an implication that
in the absence of the pulse, something will fail to happen - which is
exactly how it is. The thing that fails to happen need not be the
continuous running of an oscillator, but just its return to some
starting condition at a particular time.

I don't know how it is in all branches of electronics, but in
television, a pulse that is required to produce an output from a
subsequent circuit (rather than simply to control its timing) would be
called a drive pulse. One of the pulses from the old style sync
generators was called "Line Drive", and at least the earliest cameras
required it for the line "oscillator" to produce an output. I've even
encountered computer monitors like this, i.e. when there is no line
drive signal from the computer, horizontal scanning in the monitor
simply stops, and there is no EHT either because the same circuit does
both.

Rod.



There is a fundamental difference between a triggered timebase and a
synchronised one. In a triggerd timebase the pulse initiates the scan
and in a synchronised one it initiates the flyback.

The latter can be seen on the video waveform where the black period
after the video information ,and prior to the sync pulse, is the
"Front Porch" and the one after it, and before the video, is the "Back
Porch". The flyback takes place after the front edge of the pulse and
before the end of the back porch.

err, no. The flyback starts at the start of the blanking period, ie the
start of front porch. Flyback happens when the scanning voltage reaches it
maximum and quickly discharges to be ready for the next trigger.

--
From KT24 - in "Leafy Surrey"

Using a RISC OS computer running v5.11

Region 0 DVDs
 

In article , John Evans
wrote:
There is a fundamental difference between a triggered timebase and a
synchronised one. In a triggerd timebase the pulse initiates the scan
and in a synchronised one it initiates the flyback.

In the one that you want to call a triggered timebase, presumably if
there is no trigger pulse the scan does not take place. If that's the
case, then it doesn't seem right to call it a timebase at all, because
it isn't an oscillator that can produce an output on its own. I've seen
a computer monitor like this, but never a television set.

If you want to call this a synchronised oscillator, then how do you
distinguish it from the other sort, commonly used in line timebases,
where the oscillator free runs at the correct speed (subject to
component drift etc) but is brought into synchronism by a control
voltage derived from a phase comparator? By your nomenclature, both
types of oscillator are synchronised by the pulses, though the
mechanisms are quite different and they behave differently when the
pulses are not there. The one that you want to call a triggered
oscillator doesn't seem to be an oscillator at all, because in the
absence of pulses it would produce no output.

I know that it can be said that the sync pulse triggers ( better -
initiates) the flyback and that a triggerd timebase is synchronised
but that is not how they are defined.

By whom are they defined?

Rod.

Region 0 DVDs
 

On Fri, 29 Feb 2008 18:11:48 +0000 (GMT), charles
wrote:

In article ,


err, no. The flyback starts at the start of the blanking period, ie the
start of front porch. Flyback happens when the scanning voltage reaches it
maximum and quickly discharges to be ready for the next trigger.


Err yes!

The flyback is initiated by the negative going edge of the sync pulse
that occurs at then end of the front porch. The pulse puts the
oscillator voltage over the threshold and the oscillator resets. It
then starts the scanning part of the cycle again. It is free running
in the absense of a sync pulse.

Region 0 DVDs
 

In the one that you want to call a triggered timebase, presumably if
there is no trigger pulse the scan does not take place.

Correct.


If that's the case, then it doesn't seem right to call it a timebase at all, because
it isn't an oscillator that can produce an output on its own.

A timebase is a device that produces an output proportional to time -
hence its name. Its still a timebase whether its free running,
triggered or single shot if thats what it does.


I've seen a computer monitor like this, but never a television set.

Triggerd timebases aren't used in TV sets - thats my original point.

If you want to call this a synchronised oscillator, then how do you
distinguish it from the other sort, commonly used in line timebases,
where the oscillator free runs at the correct speed (subject to
component drift etc) but is brought into synchronism by a control
voltage derived from a phase comparator?

Surely synchronised means in step/time with. The difference between
triggered and free running is the latter "free runs" in the absence of
a pulse but the former doesn't. The are both kept in step by the
pulse. The phase comparator oscillators are free running - those that
I know of at least. The difference is that they are controlled by a
voltage derived from the pulse and not by the pulse directly.



By your nomenclature, both types of oscillator are synchronised by the pulses, though the
mechanisms are quite different and they behave differently when the pulses are not there. The one that you want to call a triggered
oscillator doesn't seem to be an oscillator at all, because in the
absence of pulses it would produce no output.

See above.


By whom are they defined?

The definition is inherent in the way the work , one needs a pulse to
make it operate and the other free runs with no pulse present. It was
taught this way (by someone who designed oscillators for TVs , RADAR ,
oscilloscopes etc) to make sure the operation was understood.. This
terminology is used on an oscilloscope, sometimes with the free
running state being called Auto Mode.

Region 0 DVDs
 

In article , John Evans wrote:
err, no. *The flyback starts at the start of the blanking period, ie the
start of front porch. *Flyback happens when the scanning voltage reaches it
maximum and quickly discharges to be ready for the next trigger.

Err yes!

The flyback is initiated by the negative going edge of the sync pulse
that occurs at then end of the front porch. The pulse puts the
oscillator voltage over the threshold and the oscillator resets. It
then starts the scanning part of the cycle again. It is free running
in the absense of a sync pulse.

In a field timebase this is more or less what happens, but not in a modern
line timebase. Line pulses don't reset anything; they are compared in a phase
comparator with a sawtooth voltage derived from the oscillator, to produce a
control voltage which is applied to the oscillator to control its frequency.
This arrangement is known as a phase locked loop or flywheel sync.

Rod.

Region 0 DVDs
 

In article , Roderick Stewart
wrote:
In article , John Evans wrote:
err, no. The flyback starts at the start of the blanking period, ie
the start of front porch. Flyback happens when the scanning voltage
reaches it maximum and quickly discharges to be ready for the next
trigger.

Err yes!

The flyback is initiated by the negative going edge of the sync pulse
that occurs at then end of the front porch. The pulse puts the
oscillator voltage over the threshold and the oscillator resets. It
then starts the scanning part of the cycle again. It is free running in
the absense of a sync pulse.

In a field timebase this is more or less what happens, but not in a
modern line timebase. Line pulses don't reset anything; they are
compared in a phase comparator with a sawtooth voltage derived from the
oscillator, to produce a control voltage which is applied to the
oscillator to control its frequency. This arrangement is known as a
phase locked loop or flywheel sync.

Flywheel sync isn't terribly modern - it's been around for at least 40
years.

--
From KT24 - in "Leafy Surrey"

Using a RISC OS computer running v5.11