Trap a sound signal on the Zx81 BUS.

Discussions about Sinclair ZX80 and ZX81 Hardware
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XavSnap
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Trap a sound signal on the Zx81 BUS.

Post by XavSnap » Mon Nov 04, 2019 7:32 am

Hello,

I have a little question.
Is it possible to interconnect the audio signal from the mic jack via the ZX81's expansion bus?
that is, plugging a K7 reader into a card, and reformatting the IRQ sound signal to read to load a program.
(like a video display, and don't use the ULA decoding process)

Thank you for your future answers.
All the best.

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1024MAK
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Re: Trap a sound signal on the Zx81 BUS.

Post by 1024MAK » Mon Nov 04, 2019 10:01 am

Hi XavSnap

I’m not sure what you are asking?

For loading from cassette tape, the ULA acts as a simple level shifter and input port. When the Z80 CPU reads from I/O port 0xFE, bit 7 is set or reset (high or low) depending on the voltage level on the ULA input pin (tape in, connected to the Ear jack socket). Just like the Memotech external keyboard, other devices (connected to the expansion port / edge connector) can override the ULA and instead supply data to the Z80 CPU when it reads I/O port 0xFE.

For saving to cassette tape, writes to any I/O port (although 0xFF is usually preferred) and reads from I/O port 0xFE causes pulses to be output to the combined TV/Tape ULA pin. These I/O accesses could be picked up on the expansion port / edge connector with the appropriate extra circuitry.

All the decoding and encoding of the signals from/to a cassette tape are done in software by the Z80 CPU.

You can bypass the ULA entirely if you use your own cassette tape reading or writing code. Then you can read from, or write to any I/O port.

Mark

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XavSnap
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Re: Trap a sound signal on the Zx81 BUS.

Post by XavSnap » Tue Nov 05, 2019 3:52 am

Thanks Mark !

A bluetooth circuit can therefore be integrated with an expansion card to remove the reader and the cord file loading (noises and read errors).

so it's not a sight-of-mind.

Cool…

:ugeek:

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Dim_75
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Re: Trap a sound signal on the Zx81 BUS.

Post by Dim_75 » Tue Nov 05, 2019 11:37 am

Hi Xav, something in preparation ???? :P :)

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XavSnap
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Re: Trap a sound signal on the Zx81 BUS.

Post by XavSnap » Thu Nov 07, 2019 2:03 am

:lol:

Yes Dim...
Ay_Original.jpg
And the daughter board:
lm3915.jpg

McKlaud
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Location: St Albans, UK

Re: Trap a sound signal on the Zx81 BUS.

Post by McKlaud » Thu Nov 07, 2019 9:33 am

it looks interesting. BUT, have you considered adding 16K RAM on it, just in case. No much software can run on 1K Zeddy. Are AY ports the same like in the ZON or are they ZX Spectrum ones?
Claudius
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XavSnap
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Re: Trap a sound signal on the Zx81 BUS.

Post by XavSnap » Thu Nov 07, 2019 10:58 am

Hi McKlaud,

Maybe my second next project…
Back_Ext.jpg

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