Gigatron Soundcard

Using, learning, programming and modding the Gigatron and anything related.
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Hans61
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Joined: 29 Dec 2020, 16:15
Location: Saxonia
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Gigatron Soundcard

Post by Hans61 »

I became aware of the SN76489 through the "Tandy 3 Voice Sound - SN76489 ISA Soundcard Project" (https://www.vogons.org/viewtopic.php?t=54249). Since it only has write registers, it is well suited for extension to lb3361 extension-retro.
I started making a sound card for this extension. I will continue to report on progress. My attempts so far can be found here:
https://github.com/hans61/Gigatron-TTL/ ... und%20card
gigatron-sn76489-schematic.png
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20220806-gigatron-soundcard.jpg
20220806-gigatron-soundcard.jpg (179.9 KiB) Viewed 1386 times
lb3361
Posts: 367
Joined: 17 Feb 2021, 23:07

Re: Gigatron Soundcard

Post by lb3361 »

Great work :-).
bmwtcu
Posts: 145
Joined: 01 Nov 2018, 12:02

Re: Gigatron Soundcard

Post by bmwtcu »

Outstanding! I didn't get what you meant by "it is well suited for extension to lb3361 extension-retro" until I saw the photo in the Pluggy Reloaded thread showing how the headers lined up. Looking forward to your updates!
denjhang
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Joined: 02 May 2021, 01:25
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Re: Gigatron Soundcard

Post by denjhang »

I recommend using a crystal with a frequency of 3.57mhz or lower, because for the SN76489, a lower crystal frequency allows a lower tone. For example, the lowest sound of SN76489 at 3.57mhz is A2.
Since I have developed many MegaMods (vintage Yamaha FM synth music IC modules) before, I can even launch sound cards for gigatron with many FM sources, such as YM2612, YM2151, YM2203, etc. But lack of software support, even if I made the hardware out, it would take a lot of time to write the music driver.
Hans61
Posts: 102
Joined: 29 Dec 2020, 16:15
Location: Saxonia
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Re: Gigatron Soundcard

Post by Hans61 »

I have no musical talent. I just wanted to see if the Gigatron could control a sound chip. I thought the SN76489 was the simplest option. Since the Gigatron can only write ports, not read them.

I hadn't gotten my board to work yet and had almost forgotten about it. I wasn't aware that the SN76489 was available with two different pinouts.
With this knowledge I have now done it.

I wrote a few simple tests in gasm and glcc. Also a simple player in glcc with which you can play VGM songs.
The player still has a lot of optimization potential. Writing the SN76489 should be integrated into assembler.
I also don't know if you can use the interrupt to write the sound data. You could then do something else in the main program.

My results so far can be found here:

https://www.youtube.com/watch?v=wv5x-WD0vzI

https://github.com/hans61/Gigatron-TTL/ ... und%20card

@denjhang I operated the SN76489 at 4 KHz because I had the crystal there and because that's how it runs on the BBC. I found projects on the Internet with 4, 3.57 and 2 MHz. I read that it also has better sound at 2 MHz. I ordered a few more quartz.
P.S. A late answer is better than none, thanks for the tip
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