Advanced Assembly Programming - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 201

sub_x deca

ldab 0,x

inx

loop cmpb 0,x

ble next

ldab 0,x

next inx

deca

bne loop

rts
E4.7 Write a subroutine that can multiply two 32-bit unsigned integers. Both the multiplicand
and the multiplier are passed to this subroutine in the stack. The caller pushes the multiplicand
into the stack fi rst and then pushes the multiplier. The pointer to the buffer to hold the product
is passed in index register X.
E4.8 Write a subroutine that can count the number of characters and words contained in a
given string. The pointer to the string to be examined is passed in X. The character count and
word count are returned in Y and B, respectively.
E4.9 Write a subroutine that can fi nd whether a given word is contained in a string. The pointer
to the word to be found and the pointer to the string to be searched are passed in X and Y, re-
spectively. This subroutine would return a 1 in B if the word is found in the string. Otherwise,
a 0 is returned in B.
E4.10 Draw the stack frame and enter the value of each stack slot (if it is known) at the end of
the following instruction sequence:

leas

2 2,sp

clrb

ldaa #20

psha

ldaa #$E0

psha

ldx #$7000

pshx

jsr sub_abc

…

sub_abc pshd

leas

2 12,sp

…
E4.11 Draw the stack frame and enter the value of each stack slot (if it is known) at the end of
the following instruction sequence:

leas

2 8,sp

ldd #$1020

psha

ldx #$800

pshx

bsr xyz

…

xyz pshd

pshx

leas

2 10,sp

…