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I got two PI zero boards, but have found little information about them.  
Perhaps someone here can direct me to the answers.

Does any one know where schematics can be found?

On the boars are pads marked "TV" and "RUN" on the front. What are these  
used for?

On the back are pads marked J5. What are those?

Thanks.

Re: R PI 0 question
Am 22.12.2015 um 20:18 schrieb lyttlec:
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TV: RCA Composite Video Output
RUN: Reset Switch

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For JTAG debugging.

--  
Robin Koch

Re: R PI 0 question
On 12/22/2015 02:52 PM, Robin Koch wrote:
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Seemed reasonable. But the zero is hard to get, and I didn't want to  
take a chance.

Is there a recommended connector to fit the JTAG pads.

Thanks again.

Re: R PI 0 question
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No - Even if there were, there's nothing you can do with it - not unless
you're an employee of Broadcom with the right equipment and data sheets.

Just forget the JTAG.

It's a Raspberry Pi - more or less equivelent to the current A+
model without the audio and composite video connectors and associated
circuitry. It runs Linux (and other OSs) and has a bunch of user
controllable GPIO pins and ports.

Enjoy,

Gordon

Re: R PI 0 question
On 12/22/2015 5:45 PM, Gordon Henderson wrote:
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The sad part of composite video is that it seems to be going away in the  
consumer market (US). I think I have (maybe) one working monitor left  
that will accept composite video, and automatically shows it in green.  
Used to have an amber one, but it died years ago.


Re: R PI 0 question
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Composite monitors, color or monochrome, are actually readily available on
eBay, etc., and plenty of LCD monitors support NTSC composite video (with
varying degrees of success).  ;-)
--  
-michael - NadaNet 3.1 and AppleCrate II:  http://michaeljmahon.com

Re: R PI 0 question
On Wed, 23 Dec 2015 01:46:08 -0600, Michael J. Mahon wrote:

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& it is available on a scart skt (do modern TV's still have these)
My Samsung TV has HDMI SCART Composite Component & VGA I do not think it  
is uncommon

for smaller form factor may monitors designed for in car DVD players have  
composite input




--  
You will be called upon to help a friend in trouble.

Re: R PI 0 question
On Tue, 22 Dec 2015 23:31:44 -0500

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Composite is a colour signal.

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I thought the sad part of composite video was that it was always a bit
crap.  But if you must use it then composite to HDMI converters are
readily available so you can view its fuzzy inaccurate colours on
your HD TV.


Re: R PI 0 question
On Wed, 23 Dec 2015 13:54:01 +0000, Rob Morley wrote:

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Composite monochrome output was common for some considerable time before  
microprocessor-based computers were capable of generating colour output,  
though the colour of the display varied.  

I always assumed that was due to the phosphor on your CRT: close  
examination of the screen on the green-screen 12" CRT I use with my 6809  
box doesn't show the pixellation that you normally see on a colour  
screen, though - it looks like a single, even coat of phosphor.

Don Lancaster's "The Cheap Video Cookbook" told you how to build a a dirt  
cheap memory mapped display. I went one better: my memory mapped display  
used a 2K block of static RAM that was part of the MPU's address map and  
included a 6845 CRTC chip, run 180 degrees out of clock phase with the  
6809 CPU so both could run at full speed without interference. The 6845  
scanned each line of RAM once for each monitor display line, passing  the  
address contents and scan line number to an EEPROM as an address and  
reading out the dot pattern for than scan line of that character into a  
shift register. The 6845 also generated the clocks needed to generate  
scan lines from the shift register content as well as triggering the CRT's  
line flyback and framing signals. This generated mono composite video: to  
produce colour would have needed more RAM than the 2KB that was used and  
was only big enough to deal with a monochrome 24 x 80 display. Colour  
would have needed at least another 2KB to hold the colour attributes,  
etc. of each byte.  

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That was a direct result of using a standard TV display: the resolution  
was limited by the TV's bandwidth or, if it was a colour TV, the size of  
the phosphor dots seriously limited the display resolution for text. Have  
a close look (from 12-18") at any colour TV (CRT, not LCD/OLED/digital  
screen) and you'll see what I mean.

A reasonable British monochrome 625 line CRT TV monitor did a pretty good  
job of handling a 24x80 display, while a standard US TV one had only 525  
scan lines and a considerably lower horizontal resolution and, as a  
consequence, struggled to show even a 16x64 display. A lot of the early  
US microprocessors used even lower horizontal resolution: IIRC 16x48  
displays were quite common (Apple II with colour TV?) and some were as  
low as 16x32 (KIM1 with Cheap Video Cookbook display?), though that may  
have had more to do with available RAM rather than TV horizontal  
resolution.


--  
martin@   | Martin Gregorie
gregorie. | Essex, UK
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Re: R PI 0 question
On 12/23/2015 7:21 PM, Martin Gregorie wrote:
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I think you over estimate the difference between the TVs and underrate  
the difference in the standards.  In the US much of the limitation was  
bandwidth in the composite format.  I added optoisolators to a TV to  
avoid the composite input and got acceptable performance with 80 chars.  
  The real issue was they were squished together a bit too much  
visually.   80 was at the TV's limit but it didn't have any trouble at  
all displaying 64 chars.

--  

Rick

Re: R PI 0 question
On Thu, 24 Dec 2015 00:21:36 -0000 (UTC), Martin Gregorie

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To echo Rob's remark, composite is a colour signal, composite means a
composition of two or more component parts, these being the basic
luminance waveform with the chrominance and reference burst
superimposed.

Obvioulsly the vertical definition is lower with fewer scan lines, but
why should the horizontal definition be worse on a 525/60 set compared
with 625/50?
It turns out that time taken to paint a scan line across the screen,
ie the active line period, excluding the blanking interval, is almost
identical for each system
625/50 = 52.0 microseconds
525/60 = 52.6 microseconds

On a mono baseband monitor intended to render TTL text there would be
nothing to gain by limiting the bandwith of the video signal.

--  

Graham.

%Profound_observation%

Re: R PI 0 question

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<snip>

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The difference may have been in the shadow mask. Most (until the  
Trinitron tubes were produced) used circular holes through which the  
three electron beams were projected onto the phosphor. If you have  
less vertical lines, you can use slightly larger holes, spaced more  
widely. This reduces the resolution in both vertical and horizontal  
directions.

I once modified a Trinitron set to provide direct input to the guns,  
so that a BBC micro could produce a better colour display. This  
bypassed the composite video limitations on bandwidth - the colour  
subcarrier required a filter to restrict the monochrome bandwidth. The  
difference in picture quality was striking.

--  
Alan Adams, from Northamptonshire
snipped-for-privacy@adamshome.org.uk
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Re: R PI 0 question
On Thu, 24 Dec 2015 03:51:46 +0000, Graham. wrote:

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IIRC NTSB used some sort of phase shift to encode the colour (with the  
amount of rotation of the phase shift selecting the next colour). As this  
alters the relative brightness of the colour guns you get a sort of  
colour blur as the electronics track round colour sequence. In any case  
the horizontal edge of a NTSB colour change is indefinite and of much  
lower resolution that the vertical colour change resolution, which is  
simply the scan line spacing. I suppose that if you grew up with NTSB  
colour you'd not consciously notice this because 'thats just how TV is',  
but if you've grown up with PAL colour encoding the lower colour  
resolution of NTSB is very noticeable.

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Economics limits the bandwidth. Back in the day[*] most people didn't use  
VDU quality displays. When the first microcomputers (IMSAI, MTS, Altai,  
SWTPC) appeared you used an ASR33 teletype or, if you had real money, a  
second hand serial terminal to talk to it. A bit later microcomputers  
grew ASCII keyboards with parallel connections and memory mapped displays  
with composite video output. Now the standard hobbyist monitor was either  
an unmodified TV set or what was effectively a TV set with the tuner  
removed (this alone improved the resolution of a monochrome display). No  
mass market TV manufacturer is going to use better components than they  
need to because higher bandwidth tubes/transistors and more accurate  
filters cost more,  

[*] This was 1975/76. I was working in NYC at the time, in the 500s on  
Madison, and so could wander over to The Computer Store on 5th, a few  
blocks up from the Empire State Bldg, at lunch time and have a play. They  
sold the brands I've listed. Commodore Pets, Trash-80s and Apple IIs were  
all a year or three later.  


--  
martin@   | Martin Gregorie
gregorie. | Essex, UK
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Re: R PI 0 question
On 24.12.15 14:26, Martin Gregorie wrote:
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The American system is called NTSC (National Television Systems
Commitee, or never twice same color).

The analog colour television sends three signals, one black-and-white,
luminance, marked Y, and two colour difference signals.

The luminance channel runs on full bandwidth (PAL: 7 MHz) and the
difference channels have limited bandwidth (PAL: 1.1 MHz). This is
like giving a full resolution black and white image and wide colour
pens. The eye is so forgiving that the result goes for full value.

The difference channels are modulated as double sideband suppressed
carrier signals on the subcarrier (NTSC: 3.58 MHz, PAL: 4.43 MHz).
To keep the signals separate, the subcarriers are copies of the same
frequency, but at 90 degree phase difference.

What makes PAL less suspectible for phase errors is that one difference
signal is inverted on alternate scan lines, so the receiver can
compenasate by averaging the phases of two lines.

--  

-TV


Re: R PI 0 question
On Thu, 24 Dec 2015 16:35:03 +0200, Tauno Voipio wrote:

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Thanks - good description. I'd noticed that the monochrome image had to  
be separate because its noticably sharper. This is particularly obvious  
if you see a YouTube capture of some old analogue NTSC footage.

Your comment about the eye being forgiving is what I meant by saying that  
those brought up with analogue NTSC probably didn't notice the colour  
blurring because 'thats just how TV is'.


--  
martin@   | Martin Gregorie
gregorie. | Essex, UK
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Re: R PI 0 question
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Actually, that's just how the human eye is.  

All modern color encoding schemes, starting with NTSC, are based upon
studies of human visual perception.  

And, though early color TV sets were less accurate in their color
rendition, this was largely a result of users idiosyncratic settings of the
"hue" (phase) and "saturation" (chrominance amplitude) controls. By the
time the Trinitron arrived, these "controls" had become mostly automatic,
and NTSC color receivers produced excellent color.  
--  
-michael - NadaNet 3.1 and AppleCrate II:  http://michaeljmahon.com

Re: R PI 0 question
On 24/12/15 17:03, Michael J. Mahon wrote:
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No they didnt. Except on predictable cable.

multi
path screwed them completely


--  
the biggest threat to humanity comes from socialism, which has utterly  
diverted our attention away from what really matters to our existential  
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Re: R PI 0 question
On Thu, 24 Dec 2015 17:23:18 +0000, The Natural Philosopher

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That reminds me of an argument I once had with a Canadian. He was
quite sure that NTSC was far superior to PAL because their sets had a
control for hew as well as saturation...

--  

Graham.

%Profound_observation%

Re: R PI 0 question
On 25/12/15 10:56, Graham. wrote:

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Ah yes, the 'how far should we take an axe to the picture' control ...


--  
the biggest threat to humanity comes from socialism, which has utterly  
diverted our attention away from what really matters to our existential  
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Re: R PI 0 question
On 12/25/2015 5:56 AM, Graham. wrote:
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What is "hew"?

--  

Rick

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