Atari XL

Sound and Music
POKE 53768,1
99
the frequency of the note produced will drop
dramatically. This is because bit 0 of the POKEY
control register (peR from now on) controls the
frequency of the clock pulses applied to the POKEY
chip. Bit 0 is usually set to 0, but when set to 1, the
frequency of the clock pulses is reduced by a factor
of about four - resulting in a much lower output
frequency.
This effect applies to all four tone channels.
The other seven bits in peR are used to control
other functions, as shown in this table.
BIT FUNCTION
0
Switch clock
from 64kHz to 15
kHz
1
High Pass Filter on Channel 1
(controlled by Channel 3)
2
High Pass Filter on Channel a
(controlled by Channel 2)
3
Adds Channel 2 to Channel 3
4
Adds Channel a to Channel 1
5 Channel 2 clock = 1.79 MHz
6 Channel 0 clock = 1.79 Mhz
7 Increases repeat rate of random
waves
POKEY Control Register Functions