[Coco] Cassette Program Loading Help Needed

[RETRO Innovations]

On 3/19/2017 12:40 AM, Darren A wrote:
> On Sat, Mar 18, 2017 at 9:56 PM, RETRO Innovations wrote:
>
>> On 3/18/2017 10:36 PM, Dave Philipsen wrote:
>>
>>> You could go about it in a completely different manner and not generate
>>> the audio using PWM.  Just generate a straight square wave and feed that to
>>> the CoCo.
>>>
>> As noted above, I thought of that, but early results were not encouraging.
>>
>> I thought for sure the resistor DAC would work, and I could get back to
>> laying out the board, but I am back to diagnosing again.
>>
>>
> Have you looked at how the MC-10 generates its cassette output?  It uses a
> single output port pin on the 6803 MCU with a simple attenuator.
Yep, looks like they sued the same final output stage as the coco (75K, 
20pF, etc.), but what I am finding is that the coco/MC-10 output is not 
suitable for the input to the coco (and I assume the mc-10).

Which is a shame, as I would be happy to wire up the exact circuit.

It is looking very confident that the coco cassette audio in expects to 
see a non-dc bias signal.  When I remove the blocking cap, the S stays 
regular, but when I put it inline, the S goes inverse after the filename 
goes out.

I think I could record the audio, if that would help.

Jim