Motorola Axiom CMD11E1 Uživatelská příručka stáhnout pdf (Strana 42)

42 CHAPTER 3. FUNCTIONS AND BIT MANIPULATIONS

JSR CLRBIT4

LDAA $00

JSR PRBINARY *PRINT AFTER CLEAR

SWI

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

; Function: CLRBIT4

; Purpose: Clears bit #4 in memory location $00

; Registers modified none

;

CLRBIT4

PSHA

LDAA $00

ANDA #%11101111

STAA $00

PULA

RTS

;; INSERT THE CODE FOR FUNCTIONS SETBIT4 RAND AND PRBINARY HERE

ORG $D000

;; ALL THE DATA ITEMS GO HERE.$

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

3.8 Toggling bits

We will now write a function that will toggle (make it zero if it was a one; make

it one if it was a zero) 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 toggle bit #4

in memory location $00. To toggle a bit, we use the eor 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

1 2 ... 37 38 39 40 41 42 43 44 45 46 47 ... 100 101

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Motorola Axiom CMD11E1 Uživatelská příručka Strana 42