VOGONS


Reply 60 of 114, by Great Hierophant

User metadata
Rank l33t
Rank
l33t

The best technical information available for the PSSJ can be found in the Tandy 1000 TL (or SL) Technical Reference Manual. You can find them here : ftp://ftp.oldskool.org/pub/tvdog/tandy1000/documents

There is also a document called TANDAC.DOC which helps explain how to make the DAC work I have attached it.

One thing I realized that in PSSJ Tandys, the DAC uses C4-C7. In non-PSSJ Tandys, those addresses would be mirrors of C0. However, it is important to note that the DAC adds another whole layer of complexity to the design because it uses an IRQ and a DMA. It also provides additional functionality to the sound generator. This functionality may never have been used by games. Also, there are BIOS calls added for the TL/SL and later machines to allow access to the DAC.

I would suggest that it would be much easier to use a Sound Blaster to emulate the Tandy DAC.

Attachments

  • Filename
    TANDAC.zip
    File size
    14.47 KiB
    Downloads
    106 downloads
    File license
    Fair use/fair dealing exception

http://nerdlypleasures.blogspot.com/ - Nerdly Pleasures - My Retro Gaming, Computing & Tech Blog

Reply 61 of 114, by carlostex

User metadata
Rank l33t
Rank
l33t
Great Hierophant wrote:

This functionality may never have been used by games. Also, there are BIOS calls added for the TL/SL and later machines to allow access to the DAC.

I would suggest that it would be much easier to use a Sound Blaster to emulate the Tandy DAC.

Trixter suggested that by disassembling a TL/RL/SL BIOS would be useful as it contains the Port/DMA info.

Reply 62 of 114, by pearce_jj

User metadata
Rank Newbie
Rank
Newbie

So to summarise, the DAC was single and only fitted from SL/TL on, and almost nothing used it except for Deskmate on those machines.

If that is all correct, I'm leaning towards dropping it and keeping with just the 3-voice tone generator.

Should be able to get the layout done by the end of the weekend.

Reply 63 of 114, by pearce_jj

User metadata
Rank Newbie
Rank
Newbie

I just noticed that the 74HCT688N is now obsolete. We can use 74LS688N for this, however it seems that we might be beginning to get to the end of projects like this without turning to CPLD etc.

Reply 64 of 114, by shock__

User metadata
Rank Oldbie
Rank
Oldbie
pearce_jj wrote:

I just noticed that the 74HCT688N is now obsolete. We can use 74LS688N for this, however it seems that we might be beginning to get to the end of projects like this without turning to CPLD etc.

Those can usually still be easily sourced ... not that the IC type should matter too much in this kind of application (apart from the correct voltage levels of course).

Current Project: new GUS PnP compatible soundcard

[Z?]

Reply 65 of 114, by Great Hierophant

User metadata
Rank l33t
Rank
l33t
pearce_jj wrote:

So to summarise, the DAC was single and only fitted from SL/TL on, and almost nothing used it except for Deskmate on those machines.

If that is all correct, I'm leaning towards dropping it and keeping with just the 3-voice tone generator.

Not quite, the DAC functionality of the PSSJ, as in 8-bit digitized sound support via interrupt-driven DMA transfers or via direct-write polling, was used in about 85 games. The DAC was also capable of acting like a fourth PSG channel with rectangle, triangle or sawtooth waves available. I do not know if this was ever used, but its doubtful. The enhanced musical features added to the 3-voice sound chip core in the PSSJ, including an extra bit for frequency division, phase synchronization for the tone channels and reduced wait states, are not known to be used. I would think emulation would take care of those few games that support Tandy DAC but not Sound Blaster.

http://nerdlypleasures.blogspot.com/ - Nerdly Pleasures - My Retro Gaming, Computing & Tech Blog

Reply 66 of 114, by pleonard

User metadata
Rank Newbie
Rank
Newbie
Great Hierophant wrote:

The DAC was also capable of acting like a fourth PSG channel with rectangle, triangle or sawtooth waves available. I do not know if this was ever used, but its doubtful.

So for example the bullet sound that occur on the title screen of Police Quest I -- it's one of the regular audio channels, not the DAC, that's creating the impact sound?

https://youtu.be/h55tKjZrb98?t=3m41s

Reply 67 of 114, by Great Hierophant

User metadata
Rank l33t
Rank
l33t
pleonard wrote:
Great Hierophant wrote:

The DAC was also capable of acting like a fourth PSG channel with rectangle, triangle or sawtooth waves available. I do not know if this was ever used, but its doubtful.

So for example the bullet sound that occur on the title screen of Police Quest I -- it's one of the regular audio channels, not the DAC, that's creating the impact sound?

https://youtu.be/h55tKjZrb98?t=3m41s

That is just the noise channel, nothing special for the TI SN 76496 3-voice sound chip

http://nerdlypleasures.blogspot.com/ - Nerdly Pleasures - My Retro Gaming, Computing & Tech Blog

Reply 69 of 114, by carlostex

User metadata
Rank l33t
Rank
l33t
pearce_jj wrote:

Quick update - the board layout has fallen victim to a flurry of Lo-tech activity, however I'm back on this now. Sorry for the delay.

No worries, we all know how to be patient. 😀

Reply 70 of 114, by HighTreason

User metadata
Rank Oldbie
Rank
Oldbie
Great Hierophant wrote:
pleonard wrote:
Great Hierophant wrote:

The DAC was also capable of acting like a fourth PSG channel with rectangle, triangle or sawtooth waves available. I do not know if this was ever used, but its doubtful.

So for example the bullet sound that occur on the title screen of Police Quest I -- it's one of the regular audio channels, not the DAC, that's creating the impact sound?

https://youtu.be/h55tKjZrb98?t=3m41s

That is just the noise channel, nothing special for the TI SN 76496 3-voice sound chip

That might hold water somehow though, maybe PWM is possible or something. The SEGA Game Gear can do that trick despite having what seems to be a rough copy of the TI SN76489 inside. See https://www.youtube.com/watch?v=9BldSK2IllU

My Youtube - My Let's Plays - SoundCloud - My FTP (Drivers and more)

Reply 71 of 114, by Great Hierophant

User metadata
Rank l33t
Rank
l33t
HighTreason wrote:

That might hold water somehow though, maybe PWM is possible or something. The SEGA Game Gear can do that trick despite having what seems to be a rough copy of the TI SN76489 inside. See https://www.youtube.com/watch?v=9BldSK2IllU

It is quite possible on the Tandy sound chip, but I am far from certain that the AGI engine was capable of it. Here is information about games that do use PWM on the Tandy :

http://nerdlypleasures.blogspot.com/2014/09/n … nd-part-ii.html

https://www.youtube.com/watch?v=I8_z_CI37JE
https://www.youtube.com/watch?v=t2N7VLF0ZQo
https://www.youtube.com/watch?v=4_j_0nbff28
https://www.youtube.com/watch?v=M2A8GbsKcYQ

http://nerdlypleasures.blogspot.com/ - Nerdly Pleasures - My Retro Gaming, Computing & Tech Blog

Reply 72 of 114, by pearce_jj

User metadata
Rank Newbie
Rank
Newbie

I've not forgotton about this, just been struggling with time but also the 3.5mm socket is proving a PITA. If anyone has a product with a published Eagle layout, that would be very helpful and I can then get this finished 😀

Reply 79 of 114, by Scali

User metadata
Rank l33t
Rank
l33t

They can be ordered here: https://www.lo-tech.co.uk/product/tandy-sound … 89-adapter-pcb/
Note that there are a few small errata, as mentioned here in the wiki: https://www.lo-tech.co.uk/wiki/Lo-tech_Tandy_ … e_Sound_Adapter

http://scalibq.wordpress.com/just-keeping-it- … ro-programming/