Nintendo DMG-01 Manual - Page 30

Timer

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2.10. Timer Game BoyTM CPU Manual 2.10. Timer Sometimes it's useful to have a timer that interrupts at regular intervals for routines that require periodic or percise updates. The timer in the GameBoy has a selectable frequency of 4096, 16384, 65536, or 262144 Hertz. This frequency increments the Timer Counter (TIMA). When it overflows, it generates an interrupt. It is then loaded with the contents of Timer Modulo (TMA). The following are examples: ;This interval timer interrupts 4096 times per second ld a,-1 ld ($FF06),a ld a,4 ld ($FF07),a ;Set TMA to divide clock by 1 ;Set clock to 4096 Hertz ;This interval timer interrupts 65536 times per second ld a,-4 ld ($FF06),a ld a,5 ld ($FF07),a ;Set TMA to divide clock by 4 ;Set clock to 262144 Hertz Page 30 V 1.01

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2.10. Timer
Game Boy
TM
CPU Manual
2.10.
Timer
Sometimes it's useful to have a timer that interrupts
at regular intervals for routines that require
periodic or percise updates. The timer in the GameBoy
has a selectable frequency of 4096, 16384, 65536, or
262144 Hertz. This frequency increments the Timer
Counter (TIMA). When it overflows, it generates an
interrupt. It is then loaded with the contents of
Timer Modulo (TMA). The following are examples:
;This interval timer interrupts 4096 times per second
ld
a,-1
ld
($FF06),a
;Set TMA to divide clock by 1
ld
a,4
ld
($FF07),a
;Set clock to 4096 Hertz
;This interval timer interrupts 65536 times per second
ld
a,-4
ld
($FF06),a
;Set TMA to divide clock by 4
ld
a,5
ld
($FF07),a
;Set clock to 262144 Hertz
Page 30
V 1.01