Motorola Axiom CMD11E1 Guía de usuario descargar pdf (Pagina 83)

7.4. THE REAL TIME INTERRUPT 83

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

; INTERRUPT SERVICE

SERVICE

; TOGGLE PA4

LDAA #%00010000

EORA PORTA

STAA PORTA

; TURN OFF THE FLAG!

LDAA #%01000000 <= This is different

STAA TFLG2

; END WITH AN RTI

RTI

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

; Connect the service to the interrupt ;

ORG $00EB ; $00EB0 WHERE THE SERVICE STARTS

JMP SERVICE ; JUMP TO WHERE THE SERVICE CODE ACTUALLY IS

7.4.1 Exercises

1. Modify the above program to generate a 61 Hz square wave by setting the

RTI interrupt rate to 61 Hz.

2. After you made the modiﬁcation, toggle PA4 every 61 interrupts (Hint, set

up a counter and initialize it to 61 in the main program. In the interrupt

service, decrement the counter. When the counter reaches zero, toggle the

pin and reset the counter back to 61). Verify that the signal you generate

is a 1 Hz square wave

3. Create a simple clock. In addition to toggling the pin, increment an 8-bit

variable called TIME. In the main loop, instead of printing Z’s, print the

variable using OUT1BSP.

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Motorola Axiom CMD11E1 Guía de usuario Pagina 83