[Coco] Cassette Program Loading Help Needed
go4retro at go4retro.com
Sun Mar 19 21:04:03 EDT 2017
On 3/18/2017 11:12 PM, Dave Philipsen wrote:
> In theory, a square wave should work. The only reason for the sine
> wave was to be more accommodating to the analog circuitry of a
> cassette recorder. You might try a square wave with some sort of
> attenuator on it to control the amplitude of the signal going into the
> CoCo. As I recall, the CoCo was somewhat sensitive to level and you
> had to tweak the volume control on the cassette player to get it to
> work reliably. You can always put a 'scope probe on the output of the
> comparator to see what it's passing (pin 13 of U14 or pin 2 of U4).
Did that today, and rewrote the code to output a 1200/2400Hz square
wave, with 68ohm resistor on output, fed into a 1uF cap to the cassette
Looking at my output versus pin 2 of the 6821, the results look
identical, so I think I am sending the right voltage levels and such.
I am concerned the problem is the last bit of the last byte sent in a
set, the 0x55. since the last half of the cycle has the output low, the
junction between the end of the last bit and the rest period is lost. I
wonder if that is the issue.
At this point, it appears I need to find a way to load an actual audio
file into the coco to see what the comparator output looks like.
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