R PI 0 question

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.
Reply to
lyttlec
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Am 22.12.2015 um 20:18 schrieb lyttlec:
TV: RCA Composite Video Output RUN: Reset Switch
For JTAG debugging.
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Robin Koch
Reply to
Robin Koch
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.
Reply to
lyttlec
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
Reply to
Gordon Henderson
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.
Reply to
Charlie
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). ;-)
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-michael - NadaNet 3.1 and AppleCrate II:  http://michaeljmahon.com
Reply to
Michael J. Mahon
& 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
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You will be called upon to help a friend in trouble.
Reply to
Alister
Composite is a colour signal.
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.
Reply to
Rob Morley
What about TV sets? In Europe all new TV sets still seem to have composite input and output, (on a horrible 21 pin connector known as a SCART)
Sets in Europe are still sold with analogue and digital tuners even though, apart from a few areas in the former Soviet Union, there is no longer any broadcast analogue TV.
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Graham. 

%Profound_observation%
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Reply to
Graham.
Analog broadcast is still around in parts of the US too. Besides, I need a way to connect my video tape player. At least if I get a new TV, the DVD player won't have to connect *through* the video tape player.
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Rick
Reply to
rickman
The Pi has two JTAG ports. The ARM JTAG port provides a standard ARM core debug TAP which means that debuggers like GDB and DS5 can breakpoint, single-step, read registers, write memory, etc. Look at OpenOCD for instance to drive it. The early Pis had JTAG debugging made awkward by various stupid pin assignments, but I hope they've fixed that on the Zero.
The VideoCore JTAG is more problematic, though some minimal reverse engineering has been achieved.
I'm unclear which port the JTAG on the Zero is. If it's the VideoCore then you're broadly correct, if it's the ARM then there's plenty that can be done with it.
Theo
Reply to
Theo Markettos
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.
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.
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martin@   | Martin Gregorie 
gregorie. | Essex, UK 
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Reply to
Martin Gregorie
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.
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Rick
Reply to
rickman
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.
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Graham. 

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Reply to
Graham.
This is an alnost exact description of the video on the Commodore PET.
They went to 2k and 80x25, with the last line used either as normal or as a status line.
With a higher number of scan lines on proprietary monitors you could have a lot better resolution. Commodore did that from the 8xxx onwards.
-- mrr
Reply to
Morten Reistad
Back in the early Apple II# days, I was in Germany. Monitors were too high in price to think about. As a result, I ended up modifying a Sony AC/DC portable TV, adding a Apple compatible composite port, and tweaking the video response to accommodate an 80 column card. That worked fairly well, until I was back in the states, and ordered a monitor. That was interesting, because the vendor shipped one with minor problems. I complained, and they told me to keep it, and they shipped a replacement that worked well. I ended up giving the extra one to another apple user. For a time, I used both the monitor for text, and a small color TV for graphics. You had to take the Apple to the TV store (KMart at the time) to make sure that the TV you wanted to use would work properly with the Apple. Not a few didn't do to well.
Back in the early 70's, there was a commercial version of Lancaster's? Glass Teletype. We used it with some of the first controller based electronic test systems bought from a now defunct company, Zentel. The systems ran from Milar/paper tape, and had an odd memory scheme that involved a ring of flip-flops. A counter kept track of where the desired data was, and it was grabbed on the fly. Core and plated wire memory was king, but horribly expensive.
Reply to
Charlie

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.
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Alan Adams, from Northamptonshire 
alan@adamshome.org.uk 
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Reply to
Alan Adams
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.
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.
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martin@   | Martin Gregorie 
gregorie. | Essex, UK 
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Reply to
Martin Gregorie
And of the display card in the original IBM PC :-) I replaced my original 16x64 display card with the 6845-based 24x80 (and rewrote the EEPROM to suit) in either 1979 or early 1980.
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martin@   | Martin Gregorie 
gregorie. | Essex, UK 
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Reply to
Martin Gregorie
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.
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-TV
Reply to
Tauno Voipio

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