DTMF.ASM: A DTMF (Touch-Tone) decoder for the EVM

This program is basically a port of a DTMF transmitter/receiver
program from the the Motorola Dr BuB 56000 software collection.
It is provided under a DISCLAMER OF WARRANTY available from
Motorola DSP Operation, 6501 Wm. Cannon Drive W., Austin, Tx., 78735.

Ported to the EVM/Leonid system by Doug Braun, N1OWU

This program is pretty straightforward.  It listens to either
the left or right channel, and when it detects a touch-tone
character, it sends it (followed by CR+LF) to the serial port.
Then a proper DTMF tone is being detected, the DCD LED will light up.

Note: This program uses registers R3/M3/N3.  Thus, it will work OK
with the enhanced N1OWU version of Leonid, but not the original
AlefNull version. If you are using the original Leonid BIOS.ASM,
you will either need to fix the code, or better yet get N1OWU's
enhanced BIOS.ASM.