Texas Instruments MSP53C391, Руководство пользователя

Страница: 48 / 109

FM Synthesis Overview
B-2
B.1 FM Synthesis Overview
FM synthesis is a technique for creating harmonically rich musical tones in a
relatively simple manner. Generally speaking, the tones generated do not
closely correspond to the tonal texture of conventional instruments; but can be
used to generate interesting and pleasant music.
The MSP53C391 and MSP53C392 can generate two channels of FM synthe-
sis. This means that a maximum of two notes can be played simultaneously.
This appendix describes the command formats used to describe the music.
B.2 FM Synthesis Format and Commands
The song to be played is coded into a file in a specified format. This file is then
assembled and the binary result is transmitted by the master microprocessor
to the MSP53C391 and MSP53C392 to play the music.
The file contains a series of BYTE or DATA statements as described in the fol-
lowing to specify the notes, instruments and other details of the music.
Each command is of the general form:
BYTE command, parameters,
…
Where command indicates the action to be taken, followed by one or more mo-
difying parameters. For example, to transpose a section of a song up by a
semitone, the following command would be written:
BYTE RTRNS,1
In this example, RTRNS is the command and 1 is the modifying parameter.
As another example, to play a note, the following command might be written:
BYTE C1,n4,n4,127
This example commands the synthesizer to play a ‘C’ note for a quarter note
duration at the maximum volume.
The formats and parameters for the different commands are described in the
following sections.
The various commands are defined in the file FMEQUM2.INC. The contents
of this file should either be copied into the start of the FM file or a copy com-
mand should be inserted at the start of the FM file to insert the values; for ex-
ample:
COPY ‘FMEQUM2.INC’