June 2000, Issue 119

The Chips are Alive with the Sound of Music
Imitatiing the Dead Melody IC

TEA FOR TWO

The interrupt routine requires less than the 64 µs that timer0 allows. If it didn’t, no other work could be done. It has enough time, in fact, that the note generation code can be duplicated to allow for a second note. The second note would be output at the same time as the first, creating harmony. In addition, a second note requires a second note table. This isn’t a problem, but it created unusual output when I entered one wrong timing bit. The first time through the tables, the notes were in time with each other. However, after the incorrectly notated note played, the two parts were out of sync. And, each time through, they grew further apart. This is where separating the table data into groups (measures) makes it easy to locate errors.