ZX81 loading of programs not working

Discussions about Sinclair ZX80 and ZX81 Hardware
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mrtinb
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Re: ZX81 loading of programs not working

Post by mrtinb » Wed Dec 26, 2018 8:48 pm

I have a TZXduino which handles .P files well.

Does it say the version of the TZXduino firmware?

I run version 1.8 and it works great with .P files.
Martin
ZX81, Lambda 8300, Commodore 64, Mac G4 Cube

repetto74
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Re: ZX81 loading of programs not working

Post by repetto74 » Wed Dec 26, 2018 8:55 pm

Hi mrtinb,

It is version 1.11. I will give a try with a P.file then ;-)

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1024MAK
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Re: ZX81 loading of programs not working

Post by 1024MAK » Wed Dec 26, 2018 10:32 pm

The type of connector fitted to the ZX81 (and for that matter the other original Sinclair computers) for both the ear and mic sockets are mono 3.5mm types. Stereo 3.5mm jack plugs are not compatible, as the contacts don’t line up correctly. So for the ZX81 end, you really do need a mono 3.5mm jack plug.

If your source device has a 3.5mm stereo socket (such as a PC sound card), I recommend this “3.5mm STEREO Jack Plug to 2 x MONO Jack Plugs SPLITTER Converter Cable Lead 1m” lead or a similar one. For loading, as long as the file is stereo, or the PC output is configured to output mono sound to both stereo channels, it does not matter which 3.5mm mono plug you use. If however there is audio on only one stereo channel, then you will have to try each plug in turn.

If the Mac uses a TRRS 3.5mm connector, you will have to get a suitable equivalent cable. Note that there appears to be no common standard for cables using TRRS 3.5mm connectors, as various manufacturers allocate different signals to the different connections...

For both modern computers and other audio sources like CD players, etc, the signal level may not be enough, as the levels are limited compared to the levels available from old cassette decks of the 1980s. So you may need an amplifier. The cheap type of powered speakers for use with a PC are normally okay, as long as they have a headphone output.

Mark

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Re: ZX81 loading of programs not working

Post by RWAP » Thu Dec 27, 2018 12:57 pm

I now that some people still mix up the EAR and MIC sockets - on a ZX81 they share the same circuit (as far as I recall), which doesn't help, but you need to ensure that to load programs, the lead is plugged into the EAR socket!

repetto74
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Re: ZX81 loading of programs not working

Post by repetto74 » Thu Dec 27, 2018 1:09 pm

1024Mak,

I have tried this morning to load some P. files of max 1K with the TZXDuino. As per this short video you can see how odd the loading is. When I push play on the TZXDuino, it starts sending data but the ZX81 video goes out ('no signal' from the LCD). I am using a video amp circuitry from JoustPerCoulomb as the ULA is one of those not having the correct back porsch and needs therefore amplification.
After data transfer has finished the video comes back with a 0/0 so nothing loaded or sometimes just rubbish parts of a program.

Before declaring the ULA as faulty I may want to look at the 'EAR' circuitry where there are a couple of resistors and a 10nF ceramic cap before the ULA pin 20 "Tape In".

https://youtu.be/nf1Ddfyp-XE

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Re: ZX81 loading of programs not working

Post by mrtinb » Thu Dec 27, 2018 1:59 pm

The strange pattern you have when loading is because of your videoconverter. You will only get the well known ZX81 video pattern with an old TV.
Martin
ZX81, Lambda 8300, Commodore 64, Mac G4 Cube

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1024MAK
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Re: ZX81 loading of programs not working

Post by 1024MAK » Thu Dec 27, 2018 5:19 pm

Yeah, the displayed image on LCD TVs and monitors (including those described as LED TVs which are really LCDs backlit by a panel of white LEDs) is not very helpful.

This is because the ZX80, ZX81, TS1000 and the TS1500 do not actually output any valid video signal during tape operations. Hence the analogue to digital circuitry and signal detection systems in a LCD TV/monitor (or a video converter) will get hopelessly confused.

The image displayed on my LCD TV is useless for trying to work out if a ZX81 is receiving a suitable cassette tape signal.

To sum up, the pictures shown in the manual are based on you using a monochrome CRT television. This is what the ZX81 etc were designed to be used with. LCDs work very differently. So the displayed image (if any) may not look the same.

It’s a case of try, slightly adjust the volume, try again, then repeat.

Don’t worry, when I try loading from tape, I have the same frustrating experience.

Mark

repetto74
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Re: ZX81 loading of programs not working

Post by repetto74 » Thu Dec 27, 2018 7:49 pm

The strange pattern you have when loading is because of your videoconverter. You will only get the well known ZX81 video pattern with an old TV.
You are absolutely right. I have hooked up a classic CRT TV to the composite and now the loading pattern looks good without any loss of video signal ;-). Anyway still cannot load anything properly. Either the program is loaded partially or either I have a 0/0 in returns. :idea: :?:
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repetto74
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Re: ZX81 loading of programs not working

Post by repetto74 » Thu Dec 27, 2018 7:52 pm

It’s a case of try, slightly adjust the volume, try again, then repeat.
I am using a TZXDuino for my testing and do not think any volume adjustment can be performed. It should work as good as it does with my ZX Spectrum. Last try is to hook up a tape recorder. I can key in a small basic program, try to save it and load it back again.
:roll:

Yes quiet frustrating :|

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Re: ZX81 loading of programs not working

Post by repetto74 » Sat Dec 29, 2018 8:37 pm

Today I tested with a tape recorder I was using with the ZX Spectrum and known as working. I keyed in a small basic program then connected the audio cable to the MIC output on the recorder and the other lead to the MIC of the ZX81. I hit PLAY and record and the tape will start spinning once the SAVE command is given but it will miserably end with a 0/0 :evil: :evil: .

Nothing is saved and nothing can be loaded here. Unless there is a failed component in the data audio circuitry I am afraid to say that the ULA may be dead for this function :(

EDIT : Just need to check again because as far as I saw on other videos a 0/0 prompt does not mean any error and the program may have been saved...

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