Atari XL

100
The Ateri XL Handbook
Bi ts 5 and 6 provide a more flexible way of
changing the clock frequency applied to channels 2
and 0, without affecting other channels. The clock
frequency is increased by a factor of nearly 28 - try
this example.
SOUND 2,200,10,15
POKE 53768,32
Note that the frequency of the output tone is much
higher after setting bit 5 of peR.
10 FOR Z=l TO 12
20 READ N
30 SOUND O,N,10,8
40 SOUND 2,N,10,8
50 FOR P=O TO 200:NEXT P
60 NEXT Z
70
SOUND O,O,O,O:END
100 DATA 251,230,217,204,193,182,
173,162,153,144,136,128
This program plays ascending notes on two
channels at once. If you add the line:
45 POKE 53768,32
bi t 5 of the peR is set, increasing the clock
frequency applied to channell - try it and see!
This method of increasing the frequency of the
output tone is rather crude, and the peR provides
facilities for more accurate control of frequencies.
In normal use we are restricted to 256 different
frequencies per channel, since the frequency
register for each channel consists of only eight bits.
This restriction means that many frequencies
cannot be achei ved. However, peR hits 3 and 4