INT 15 - TopView - "SOUND" - MAKE TONE
AX = 1019h
BX = frequency in Hertz (0000h = silence)
CX = duration in clock ticks (18.2 ticks/sec)
Return: immediately, tone continues to completion
Notes:  if another tone is already playing, the new tone does not start until
completion of the previous one.  Up to 32 tones may be queued before
the process is blocked until a note completes.
in DV 2.00, the lowest tone allowed is 20 Hz
if CX = 0, the current note is cancelled; if BX = 0 as well, all queued
notes are also cancelled

See also: 1673

151019 - TopView - "SOUND" - MAKE TONE