Posted By
IstvanV
on 2017-04-01
11:20:52
|  Re: Revival of interesting 'n' funny stuffs
The internal DAC in the Enterprise actually has a resolution of 6 bits per channel, and in practice it is implemented with a simple resistor ladder that can be inaccurate. There are eight 6-bit volume control registers (4 left/4 right), but not all of these can be used for PCM playback, because one of the generators can only output noise. So, the D/A possibilities include:
- only one volume register per stereo channel, this is the "official" D/A mode (disables output from the tone/noise generators)
- high frequency square wave on one or more channels, this allows up to 6 PCM streams in stereo
- one or two sound generators can output a constant logical high level with some tricks, 4 channel playback is possible this way, but without the possible disadvantages of using high frequency square waves
Timer interrupts at a programmable frequency also use one of the tone generators.
There is currently no actual external DAC hardware, although references to one with 4 8-bit channels (2 left/2 right) can be found in an old MOD player, perhaps it was built only as a prototype. Anyway, I added it to my emulator since it is easy to emulate.
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