Commodore VIC-20 - Page 257

Chapter 7: Sound 243
Programming Rhythm
Programming rhythm on the VIC is much like programming the train
sound
we made earlier. Let's start with a simple drum sound.
10 POKE 36878,15
20 POKE 36877, 229
30 FOR 1=0 TO 25:NEXT
40 POKE 36877,0
50 FOR 1=0 TO 250:NEXT
60 POKE 36877,229
70 FOR 1~0 TO 25:NEXT
80 POKE 36877,0
90 FOR 1=0 TO 250:NEXT
100 POKE 36877,129
110 FOR 1=0 TO 125:NEXT
120 POKE 36877,O
130 FOR 1=0 TO 650:NEXT
140 OOTO 20
By using the low tone register as follows we can add a bass drum:
100 FOR D=128 TO 133
110 POKE 36874,D
120 NEXT
130 POKE 36874,0
Changing the loop variables will vary the speed of the rhythm.
50 FOR 1=0 TO 125:NEXT
90 FOR 1=0 TO 125:NEXT
140 FOR 1-0 TO 650:NEXT
By adding some READ statements to the rhythm program we can
include a melody. Here's the complete listing.
1 DATA 0,0,0,0,0,0,237,239,240
2
DATA 240,239,239,237,237,237,239,240
3
DATA 243,239,240,237,237,999
10 POKE 36878,15
15 READ A:IF A-999 THEN 200
16 POKE 3687!5,A
20 POKE 36877,229
30 FOR 1-0 TO 25:NEXT
40 POKE 36877,0
50 FOR 1=0 TO 123:NEXT
60 POKE 36877,229
70 FOR 1=0 TO 23:NEXT
80 POKE 36877,O