[Coco] Cassette data format

[Mark J. Blair]

On Aug 25, 2013, at 03:32 , Ciaran Anscomb <cocomalt at 6809.org.uk> wrote:
> The cycle durations actually vary quite a bit depending on where in
> the output it is - the first bit of any byte will be slightly longer,
> as there's a bit of setup involved, etc.  Conversely, the "ideal" cycle
> durations to fall exactly in the middle of the recognition window during
> reading vary depending on which bit is being read...  I have some notes
> from old code:
> 
> /* The "ideal" pulse widths vary according to where they are:
> *
> * Leader cycle:            68 + n0 * 28, 5 + n1 * 28
> * First byte cycle:        81 + n0 * 28, 5 + n1 * 28
> * Subsequent byte cycles: 120 + n0 * 28, 5 + n1 * 28
> * Other bit cycles:        67 + n0 * 28, 5 + n1 * 28
> */

Cool! Thanks!


I wonder why they bothered to use a DAC for cassette output instead of just wiggling a digital output. Since the reader only looks at edge crossings, I'd think that sending a square wave to the cassette recorder should work just fine... assuming that the cassette recorder doesn't misbehave when it sees a square wave, i.e. ringing heavily on the edges.

-- 
Mark J. Blair, NF6X <nf6x at nf6x.net>
http://www.nf6x.net/