Motorola Axiom CMD11E1 Guia do Utilizador descarregar pdf (Página 85)

7.5. THE OUTPUT COMPARE INTERRUPT 85

SERVICE

; TOGGLE PA4

LDAA #%00010000

EORA PORTA

STAA PORTA

; TURN OFF THE FLAG!

LDAA #%01000000 <= This is different

STAA TFLG1

; END WITH AN RTI

RTI

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

; Connect the service to the interrupt ;

ORG $00DC ; $00DC WHERE THE SERVICE STARTS

JMP SERVICE ; JUMP TO WHERE THE SERVICE CODE ACTUALLY IS

Verify that the above code also generates a 30.5 Hz square wave. Now we can

reset the alarm to get a diﬀerent frequency. For example, if we modify the service

routine as follows, we will get an interrupt every 2000 clock ticks or every 1 ms

for a 1 K Hz signal.

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

; INTERRUPT SERVICE

SERVICE

; TOGGLE PA4

LDAA #%00010000

EORA PORTA

STAA PORTA

; TURN OFF THE FLAG!

LDAA #%01000000

STAA TFLG1

1 2 ... 80 81 82 83 84 85 86 87 88 89 90 ... 100 101

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