Motorola Axiom CMD11E1 Guide de l'utilisateur télécharger pdf (Page 41)

3.7. CLEARING BITS 41

SETBIT4

PSHA

LDAA $00

ORAA #%00010000

STAA $00

PULA

RTS

;; INSERT THE CODE FOR FUNCTIONS RAND AND PRBINARY HERE

ORG $D000

;; ALL THE DATA ITEMS GO HERE.

;;;;;;;;;;;;;;;;;;;;;;;end of code ;;;;;;;;;;;;;;;;;;;;;;;;

3.7 Clearing bits

We will now write a function that will clear a particular bit in some memory

location. The function should modify the value in the memory in such a way that

it only aﬀects the speciﬁc bit without changing any other bit. For deﬁniteness,

we will clear bit #4 in memory location $00. To clear a bit, we use the AND

instruction. Write the following program, and test it by repeating the call to

$C100 from the BUFFALO prompt.

;;;;;;;;;;;;;;;;;;;;;;;start of code ;;;;;;;;;;;;;;;;;;;;;;;;

;; Insert standard buffalo equates here

ORG $C100

JSR OUTCRLF *NEED THIS FOR OUTPUTS TO LINE UP!

JSR RAND

STAA $00

JSR PRBINARY *PRINT BEFORE

JSR SETBIT4

LDAA $00

JSR PRBINARY *PRINT AFTER SET

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Motorola Axiom CMD11E1 Guide de l'utilisateur Page 41