[Coco] Cassette Program Loading Help Needed

[Dave Philipsen]

What does the output of the AVR look like going to the CoCo?  If the 
signal is coming out with a high frequency component due to the way the 
PWM works it will trigger undesirable zero-crossings in the comparator 
input on the CoCo.  You could try increasing the value of the resistor.

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.

Dave


On 3/18/2017 10:11 PM, RETRO Innovations wrote:
> On 3/18/2017 10:05 PM, Arthur Flexser wrote:
>> Maybe the program wants CLOADM rather than CLOAD?
> I doubt it, because the data was saved via CSAVE
>
> At the very least, I'd expect the filename to show.
>
> I think I see the issue, but not sure how to fix.
>
> AVR running at 8MHz
> PWM in 8 bit mode
> 31250 PWM cycles per second (8000000/256)
> Using two patterns for 1200Hz and 2400Hz sine waves:
>
> const uint8_t _2400Hz[] = 
> {0x0,0x11,0x40,0x80,0xbf,0xee,0xff,0xee,0xbf,0x80,0x40,0x11};
> const uint8_t _1200Hz[] = 
> {0x0,0x4,0x11,0x25,0x40,0x5f,0x80,0xa0,0xbf,0xda,0xee,0xfb,0xff
> ,0xfb,0xee,0xda,0xbf,0xa0,0x80,0x5f,0x40,0x25,0x11,0x4};
>
> Output is 0-5V swing, run through a low pass filter (68ohm to 1uF, 
> with other end of cap to ground.)
>
> However, the output is very choppy, and I think it is messing with the 
> internal comparator
>
> Anyone have ideas on how to clean the output up?  I can go to a 6 bit 
> Resistor D to A, but it'll eat up way too many pins on the design.
>
> Jim
>