Soft Config of vLA81

[1024MAK]

The border is the non-text area at the top, bottom, left and right of the screen. The size depends on if the normal ROM code is being used, or if a custom display driver is being used. Normally it’s exactly the same colour as the text background, hence why there is very little discussion about it. But it does not have to be this colour. It can be the text colour.

I’m happy that you are making a clone, as that makes answering the question much easier!

So, answering your earlier questions, yes the short machine code program is all you need. If you are writing your own operating system, just put it in the start-up section, or have it as a subroutine that can be called.

If you are making a clone, depending on how you are making it, that does effect which way to proceed. Are you intending to use an original Sinclair Ferranti ULA, then the ZX8-CCB is the best solution.

If you are designing your own circuitry to replace the ULA, then you can easily select a black background with white text if you want.

Mark

[xubuntu]

Hi Mark ! Thank you! You are so kind !

We decided to go with the VLA81 as it solves many problems at once! No ttls, and no zx8-ccb.

Yes we are making a kind of very primitive operating system and we would like to have a black background in order to avoid the 1st impression that this is a zx81 clone! Which is after all; although we changed so many things that the only thing that really stamps it as an zx81 clone is the vla81.

What is the next "retro" / minimal chip we could use for graphics other than the vla ?

Let's forget about its other functionalities and assume we need a simple graphics chip.

I mean, not the super advanced graphics chip that the 8bit guy used for this x16 project.... something older and more simple... ? Is there anything ?

Thanks again !

[xubuntu]

Is there a way to produce sounds or a beep without using a sound chip?

Is there a way to produce a beep with the vla and the z80 ?

[mrtinb]

What is the next "retro" / minimal chip we could use for graphics other than the vla ?

…

I mean, not the super advanced graphics chip that the 8bit guy used for this x16 project.... something older and more simple... ? Is there anything ?

If you would rather have your video out on LCD or VGA and not on Composite, you can use an ESP32 with this firmware, that converts the video to LCD or VGA.

https://github.com/holmatic/zx-iot-video

[1024MAK]

There were rather surprisingly, not many graphics/video chips in the 1980s or thereabouts. Most computers manufacturers either used the Motorola 6847, one of the Texas Instruments TMS9918/9918A//9928A/9929A range, or some custom video chip. Sometimes using the Motorola 6845 (or equivalent / variation of), a display controller to provide some of the video system in conjunction with a custom video chip or with some 74 series logic and a RAM or ROM chip to provide the character pixel data.

In the ZX Spectrum 16K/48K/+ Sinclair used a bigger ULA which does all the video functions without needing the help of the Z80. It does need a separate colour encoder chip to produce the colour carrier for composite video. In the ZX Spectrum 128K and the +2 (grey), an even bigger ULA is used, this still generates the same type of video display, but outputs RGB instead.

These ZX Spectrum ULA chips also provide simple sound systems.

I mention these, as the same person that makes the vLA81 also makes the vLA82, vLA82S+ and the vLA128.

For simple sound, all you need is a single digital output. Use a flip-flop of latch so that the last state written by the Z80 is retained. Then from the output pin of this chip, use a resistor to either control a transistor, the transistor in turn switches a loud speaker or a piezoelectric disc/buzzer. Or use a simple resistor network to feed an audio output socket. To make audio sound, use a machine code routine to switch the digital output between logic 0 and 1 at a suitable rate, toggling it at an audio frequency, such that you get the wanted sound note.

Alternatively you can use a electronic buzzer which makes it’s own audio frequency sound when it’s switched on. Now the Z80 only needs to write to the flip-flop of latch to turn it on rather than having to toggle it at an audio frequency.

Mark

[1024MAK]

Is there a way to produce a beep with the vla and the z80 ?

If you mean the vLA81, not at the same time as generating a video picture.

It is possible for a vLA81 to produce sound. Machine code can toggle the video output pin at audio rates, and hence after going through a simple resistor/capacitor filter, you can get sound.

Mark

[xubuntu]

I want sound alongside with graphics, so the vla sound option is exluded. Let's exclude also the buzzer option for the moment.

I would like to attach a JACK IN on my pcb and connect there earphones or a small speaker.

What is the easiest way to hear SOMETHING with my earphones?

What do I need? I need a single digital output as you said, which is also called a IO decoder chip, if I am not mistaken.

And this chip will only be connected to the cpu ?

[mrtinb]

See Project 5 in this book.

https://archive.org/details/easyaddonproject0000bish

[1024MAK]

An example of an interface board as used with the ZX81 is here and here

This design uses memory mapped addressing, but I/O port addressing is more appropriate if only machine code will be used. Replace the /MREQ line with the /IORQ control line. Don’t include the transistor and associated circuitry that feeds the /RAMCS line. Chose different address lines (preferably A1 to A7) so that 8 bit OUT instructions can be used.

The circuitry to feed the audio output connector socket for line out could be something similar to this:

The values are appropriate as I have not had the opportunity to work them out properly or test this design in practice. But it gives you an idea. The output from the logic chip is on the left, shown as a 1kHz Square wave source. The audio output is on the right after the capacitor.

I’ll post more on driving a speaker or headphones later.

Mark

[1024MAK]

Circuit for driving a simple loudspeaker, earphones or headphones:

The loudspeaker, earphones or headphones connects between the transistor emitter and 0V/GND. The impedance of these should be 8 ohms or greater. The transistor should be rated for the current needed, I suggest a 2N2222 or similar. The left hand resistance can be a variable type to change the volume.

Mark