SUCCESS OF TIMEX COMPUTERS

General Chit Chat about Sinclair Computers and their Clones
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Paul
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Re: SUCCESS OF TIMEX COMPUTERS

Post by Paul »

I know I am too picky.
But again I have to state that PAL/NTSC are Color definitions.
The Zeddy only outputs monochrome video and so can output neither PAL nor NTSC.
It can only output some sort of monochrome video (not matching ANY standards) in 50 Hz or 60 Hz.
Many TVs in the past(TM) accepted this (2C184 ULA output) as a valid input. Then Color TVs became more common which refused to accept this output.
So the 2C210 ULA was introduced that added a defined Black level at the beginning of each line. Most Color TVs in the past accepted this (still none standard) video signal (because they worked analogue and omitted any validation).
Modern TVs are digital and only accept well defined standard signals that Zeddy can't deliver.
kind regards Paul
In theory, there is no difference between theory and practice. But, in practice, there is.
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PokeMon
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Re: SUCCESS OF TIMEX COMPUTERS

Post by PokeMon »

I disagree in this point based on some only superficial informed guys - probably a handful of users. :mrgreen:

To be more precise, PAL and NTSC are only some basic classifications of video standards but include also specifications for video transmission standards which is a bit different. To be more complicate, there is PAL also existing with NTSC like format (525 lines) which is known as PAL-M. So what is this now ? Is it PAL or NTSC ? In fact it is both. And it is standardized as well. This is standardized in the ITU BT 470-7, which is quite the same as the BT 470-6 as shown below:

https://www.itu.int/dms_pubrec/itu-r/re ... !PDF-E.pdf

And it becomes more complicate regarding transmission variants over the air and using variants like PAL B/G, D/K, I or N defining different channel bandwidth used for transmission or position of audio sub signal. So the basic definition between NTSC and PAL is not very sharp and more seen as consumer standards then detailed technical standards. Who ever could ask for a TV compatible to the BT470 standard ? Try that, ask your media markt seller next time. ;)

And see here PAL-M (which is still used in Brazil).
https://en.wikipedia.org/wiki/PAL-M

When reading further in the document you can see that this is applicable to monochrome video (transmission) as well. Oh wonder, how can that be for a color standard ? The answer to this question is quite simple, the colour enhancement of video signals was made in a way to be compatible to the still existing monochrome video signals and transmission standards from the pre-1960 area.
(this document) ... recommends
1 that, for a country wishing to initiate a conventional monochrome television service, a system using 525- or 625-lines as defined in Annex 1 is to be preferred;
2 that, for conventional monochrome 625-line systems, the video-frequency characteristic described in Recommendation ITU-R BT.472 is to be preferred;
3 that, for a country wishing to initiate a conventional colour television service, one of the systems defined in Annex 1 is to be preferred.
So this document is applicable to monochrome video signals as well as for colorized video signals and monochrome has to be seen as a substandard of ITU BT470 which meets the requirements only partly in this case. And in fact this standard was derived from the older EIA standard RS-170 which did cover only monochrome signals (as no colour signal standard where existing during the early 1950ies).
This is hard to find on the internet as it is quite too old.
http://www.epanorama.net/documents/video/rs170.html

There is quite useful video standard information supplied in this document from Maxim Integrated to video signal standards and variations.
And take note of the following statement:
The broadcast graphics format is specified by government agencies such as the FCC in the US and the ITU in Europe, while the graphics format is specified by industry or company standards. Originally, both formats shared a common baseband signal structure, specified in EIA-RS-170,1 but that changed when color was added to broadcast TV in 1953.
https://www.maximintegrated.com/en/app- ... vp/id/1184


So despite this stuff, the statements are wrong, that the definition of monochrome video signals are not covered from the NTSC and PAL standards published in the latest ITU BT470 document. It is also wrong, that the output signal does not match ANY standard video signal. It does match the monochrome defined signals and even if not all monochrome aspects are covered like frame coding it is compatible to the standards existing in 1980. Frame coding is not necessary when both contents of the odd and even frames are identical like it is in the used video format with just 192 lines, divided into 192 used lines for every frame. Even for old films from the 1950 and 1960, maybe even in the early 1970 this fact isn't much important. And as all old TV's are based on analogue video technique they all accepted a video signal with uncoded (one long vertical sync) frames very well. Effects show up here only for higher resolutions like 384 or 512 visible/used lines.

The reason why modern colour TVs tend to refuse older video signals are mostly found in unmet timing requirements regarding horizontal and vertical frequencies using digital chips inside looking for a standard conforming video signal. The BT470 defines strong timing requirements with about 0.02% or 0.05% precision of horizontal or vertical frequency. There might also be a refuse possible with uncoded frames as well. I would see, that the standards became some harder over the time or more and more precise (using crystals instead of resonators are manually trimmed R/C circuits inside). Unfortunately I have no access to the oldest standards but I might take a look in a historical book archive if I ever have a chance.

I am quite sure, that the first TV's but also many TV's from the 70ies and 80ies are not even 100% compatible with the defined standard - so who cares if Clive Sinclair met it to 100% if tested on available hardware ? And remember, that in the past the TV's where simply synchronized (50/60 Hz) with the power grid from the local electricity provider. What do you think how much close was this to the standard ?

The last point with the missing back porch on the 2C210 ULAs showed up significantly only during direct video transmission as the RF transmitted signal was a bit better seen due to technical conversion/restoring during demodulation. A good workaround is changing contrast and brightness settings which may effect other video sources and may a bit uncomfortable only. And as all systems can be improved over the time, Sinclair did with the newer ULA. As they did with the former ZX80 (replaced through ZX81).

Last but not least, the point that the Sinclair products could be run on ANY TV sold in the area 1970-1990 shows that it did met the standard, at least an industrial standard. This is the only thing what counts. And that something is not compatible with newer (future) standards happens all the time. That's why the EU was founded which has standards even for pets and vegetables. Even if they don't understand that stuff. :mrgreen:
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1024MAK
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Re: SUCCESS OF TIMEX COMPUTERS

Post by 1024MAK »

The "standards" quickly evolved over time as the technology of both broadcasters TV equipment and consumers TV receivers improved. Further, as more TV channels were wanted, so the standards changed to reflect the changes to bandwidth so more channels could fit in the allocated space in the spectrum. Colour of course changed things again. Indeed the UK for rather a long time actually had two TV systems in use. The 625 line was our second system (the earlier one being 405 line / System A).

And up until analogue transmissions were superseded by digital, the standards were adjusted slightly for various reasons.

But getting back to ZX81 and TS1000 computers, although the terms PAL and NTSC are very often used to describe the video signal from them, I prefer to use 625 line 15625Hz 50Hz (System I) for the UK and 525 line 15750Hz (15734Hz for NTSC colour) 60Hz (System M) for the USA.

As stated above, the fitting of R30 decides if the Sinclair ROM uses 50Hz or 60Hz video. But machine code programs can ignore this if they want and generate their own video. So a USA TS1000 could still generate a 50Hz video picture even with R30 fitted... ;)

Mark
ZX81 Variations
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PokeMon
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Re: SUCCESS OF TIMEX COMPUTERS

Post by PokeMon »

1024MAK wrote: The 625 line was our second system (the earlier one being 405 line / System A).
Interesting - I never heard about that.
I can not believe that this resolution has still been supported till the mid 80ies. :shock:
The 405-line monochrome analogue television broadcasting system was the first fully electronic television system to be used in regular broadcasting.

It was introduced with the BBC Television Service in 1936, suspended for the duration of World War II, and remained in operation in the UK until 1985.
And there has been a 441 line system in Italy as well and a 819 line system. Curious.

Interesting is the 180 line system for the very first (pre-war) TV transmissions or the 90 lines for the very very first TV's.
I think I have to look for a good TV history museum somewhere ... 8-)
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PokeMon
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Re: SUCCESS OF TIMEX COMPUTERS

Post by PokeMon »

I am a bit worried that I get addicted to old TVs one time.
But where get the space for them. :?
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blittled
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Re: SUCCESS OF TIMEX COMPUTERS

Post by blittled »

I'm a little late for the party. I remember an Eckerd's Pharmacy in my hometown but didn't realized they sold the TS1000. My parents got me one at a promotion at a local grocery store in 1983. If you had receipts totaling $100 you could buy the TS1000 with a 16K RAM pack for $99.95.

What was the difference of the US version of the ZX81? I know it works with 60Hz NTSC since I have both the ZX81 and TS1000 and they work on the same TV. I'm not at my ZX81 so I can't check the RAM but does it come with 1K and is it shielded?
2X Timex Sinclair 1000, ZX81, ZX80Core, 5X 16K Ram Pack, ZXBlast, ZX P file to Ear Input Signal Converter, Elf II
swensont
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Re: SUCCESS OF TIMEX COMPUTERS

Post by swensont »

> I'm not at my ZX81 so I can't check the RAM but does it come with 1K and is it shielded?

The ZX81 came with 1K and the T/S 1000 came with 2K. Once the 16K ram pack was installed, then they both had just 16K (the internal memory was switched off). My first ZX81 died with a keyboard problem. It replaced it with a T/S 1000 and it worked fine with the original Sinclair 16K pack. The printer was the 2040, which worked with both systems.
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1024MAK
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Re: SUCCESS OF TIMEX COMPUTERS

Post by 1024MAK »

And just to confuse you even more, the PCB of the ZX81 is designed to take 2k RAM chips if needed...

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
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