[Coco] Homebrew CoCo Games

[Zippster]

Looking closer (at the CoCo1 setup, I would assume the others follow a similar setup),
the 2 selector lines do control both the joystick and sound.  It looks like Darren is right that 
reading the joysticks would interrupt sound.  Switching between joystick inputs will also switch
the sound source.

So, maybe an output jack would not be such a bad idea after all.

- Ed


> On Dec 14, 2015, at 12:48 PM, Zippster <zippster278 at gmail.com> wrote:
> 
> 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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>