Casio FX-8000G Uživatelský manuál stáhnout pdf (Strana 14)

Black Magic Composer14

graphics mode change is to inform Basic about the lowered memory top, and to free the memory area

by moving the graphics data to it's new, lower, location, making the area above it free to use. Make

sure your basic program will still function with the lesser memory!

This way works for Atari-Basic, aswell as for Turbo-Basic. (But Turbo-Basic will give you a higher

memory location, more memory, and higher overall execution speed.)

19 Using songs in Assembly

Using songs within Assembly, is somewhat easier than using it in basic, because you can use any

starting adress, aslong as it goes along with system equates and your program.

Calling the sound routine will work best from the VBlank interrupt. But for good order, a call to it every

50th of a second should do. Before running a tune, it should be initialised anyway, which will also

select the song to play.

If a song has samples, the according routine should also be called from the main program. It'll play

the digi sounds untill a flag called "STOP" is set to a non-zero value. This flag is located at the

module start adress+9. The only thing to keep in mind otherwise, is that the quality of the samples

degrade by lessening the CPU load, aswell as the complexity of the display list.

A simple assembly program to call the sound module would be something like this, in BIBO-

Assembler:

00010 ; Starting adress of the music module = $4000

00020 ; Song #1 has samples!

00030 ;

00040 .or $0600

00050 ;

00060 INIT LDA #1 ;Initialise music routine, song is=1

00070 JSR MROUT

00080 LDA #VBI ;Set Vertical Blank Interrupt

00090 STA 548

00100 LDA /VBI

00110 STA 549

00120 LDA #0 ;Stop flag. Clear before running a song.

00130 STA STOP

00140 JSR MROUT+6 ;Play samples (Until STOP is set)

00150 LDA #$E4 ;Reset VBI vector

00160 STA 549

00170 LDA #$62

00180 STA 548

00190 LDA #0 ;Silence tone generators.

00200 JSR MROUT

00210 RTS

00220 ;

00230 VBI JSR MROUT+3 ;Call music routine

00240 LDA 53279

00250 CMP #6 ;Start pressed?

00260 BNE .1 ;Local label use

00270 LDA #1

00280 STA STOP

00290 .1 JMP $E462 ;Continue with the original VBI routine.

00300 ;

1 2 ... 9 10 11 12 13 14 15

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