[Coco] Homebrew CoCo Games

[Zippster]

I only traced it back as far as the switches.  I didn’t look at the control lines yet.

Is there a data sheet for the DAC?  The only thing I could find was a block diagram.

- Ed


> On Dec 14, 2015, at 12:24 PM, Darren A <mechacoco at gmail.com> wrote:
> 
> On Sun, Dec 13, 2015 at 10:34 AM, Zippster wrote:
> 
>> There is no additional overhead for the CoCo after the AY (or whatever)
>> has done it’s part and the signal is put on the SND IN line at the cart
>> port.
>> 
>> It’s all analog from there.  The cart port sound in line is then mixed with
>> the DAC output at the DAC in the case of the CoCo 2/3, or at the
>> MC14529B (between the DAC and the modulator) in the case of the
>> CoCo1.
>> 
>> Nothing would really be gained by a separate jack on the cart except
>> another output jack, one that would be missing whatever the DAC would
>> have contributed to the signal.
>> 
>> This is my understanding from the schematics, data sheets, etc.
>> 
>> - Ed
>> 
> 
> 
> 
> I don't believe there is any mixing of the DAC audio with the cartridge
> port SND line.  There are four audio sources; the DAC, the Cassette port
> input, the cartridge port SND line and the single-bit sound line. The first
> three are routed through an analog switch so only one is active at a time.
> The single-bit sound can be mixed with one of the other sources.
> 
> The selector lines for the analog switch are controlled by a couple of
> outputs on PIA0. These are the same lines used to select the joystick axis
> for sampling. If you have a device playing sound through the cartridge port
> and want to be able to read the joysticks at the same time then sound
> interruption would likely be an issue.
> 
> - Darren
> 
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