Motorola Axiom CMD11E1 Guía de usuario descargar pdf (Pagina 84)

84 CHAPTER 7. INTERRUPT PROCESSING

7.5 The output compare interrupt

The HC11 has 5 OCx interrupts. These are like alarm clocks. You set a desired

’alarm’ time and when the clock matches the alarm setting, the OCxF ﬂag will be

turned on and could then generate a request for service. Note that if you do not

change the alarm setting, you will still get an interrupt every 32.768 ms. However,

having the alarm gives you greater ﬂexibility. First a co de that does not change

the alarm setting and hence generates 30.5 Hz square wave.

; Various defines go here ...

ORG $3000 don’t forget the $

ME FCC /Your name/

FCB 10

FCC /ECE 372/

FCB 10

FCC /Date the program was last changed/

FCB 10, 10, 4

ORG $2000 DONT FORGET THE $

LDX #ME

JSR OUTSTRG ; MAKE SURE YOU HAVE EQU FOR OUTSTRG

LOOP1

; Enable OC2 interrupt by setting OC2I (bit#6 in TMSK1)

SEI

LDAA #%01000000 <= This is different

STAA TMSK1

CLI

; Now go about your business of printing Z’s

LDAA #’Z’

LOOP JSR OUTA

BRA LOOP

; End of main program

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

; INTERRUPT SERVICE

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Motorola Axiom CMD11E1 Guía de usuario Pagina 84