found an overview here: http://nerdlypleasures.blogspot.com/2015/10/t … sound-chip.html
and details here: ftp://ftp.oldskool.org/pub/tvdog/tandy1000/sound/snd_loc.txt

The DAC functionality was part of the custom PSSJ chip. It has both DMA and direct read/write (looks like the same register is used to access a joystick port as well)

Dosbox supports Tandy DAC, doesn't it? That might give you some insight if you can read the code.

I better know how it work now.
Unfortunately, it use a DMA controller PIN that is not on the ISA Bus. (TC)

There are ISA Cards with the PSSJ on it,
http://www.vcfed.org/forum/showthread.php?643 … PSSJ-ISA-Boards

Did not manage to get my hands on one yet..

Hi,

does anyone own Schematics for Tandy Machine with DAC ?
Maybe someday i could find a real tandy.

Thanks

Matthias

FreddyV wrote on 2020-10-05, 08:24:

Unfortunately, it use a DMA controller PIN that is not on the ISA Bus. (TC)

It is on the ISA bus, although some sources may call it differently. TC ("terminal count") aka EOP ("end of process") is on ISA pin B27.

matze79 wrote on 2021-06-26, 11:09:

Hi, […]
Show full quote

Hi,

does anyone own Schematics for Tandy Machine with DAC ?
Maybe someday i could find a real tandy.

Thanks

Matthias

Here are links to the Technical Reference Manuals for the Tandy 1000 SL & TL both have a schematic section.

ftp://ftp.oldskool.org/pub/tvdog/tandy1000/do … ents/sltech.zip
ftp://ftp.oldskool.org/pub/tvdog/tandy1000/do … ents/tltech.zip

mkarcher wrote on 2021-06-26, 13:23:

It is on the ISA bus, although some sources may call it differently. TC ("terminal count") aka EOP ("end of process") is on ISA pin B27.

Right, so it is possible 😀

To be compatible with the Tandy DAC, you need to add the DMA functions as well.

The Tandy DAC DMA is simple : One register containing the output frequency, one for the amplification and one to Start/Stop the output.
Plus an IRQ when at the DMA buffer end (STOP when the DMA TC signal is active as we don't send the buffer size to the DAC registers)