HCS12 Assembly Programming - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 70

N equ 20 ; array count

org $1000 ; starting address of on-chip SRAM

arrmax ds.b 1 ; memory location to hold array max

org $1500 ; starting address of program

movb array,arrmax ; set array[0] as the temporary array max

ldx #array 1 N 2 1 ; start from the end of the array

ldab #N 2 1 ; use B to hold variable i and initialize it to N 2 1

loop ldaa arrmax

cmpa 0,x ; compare arrmax with array[i]

bge chk_end ; no update if max_val is larger

movb 0,x,arrmax ; update arrmax

chk_end dex ; move the array pointer

dbne b,loop ; decrement the loop count, branch if not zero yet

forever bra forever

array db 1,3,5,6,19,41,53,28,13,42,76,14,20,54,64,74,29,33,41,45

end

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2.6.6 Decrementing and Incrementing Instructions
We often need to add 1 to or subtract 1 from a variable in our program. Although we can
use one of the add or sub instructions to achieve this, it would be more efficient to use a single
instruction. The HCS12 has a few instructions for us to increment or decrement a variable by 1.
A summary of decrement and increment instructions is listed in Table 2.5.

Decrement Instructions

Mnemonic Function Operation

dec <opr>
deca
decb
des
dex
dey

Decrement memory by 1
Decrement A by 1
Decrement B by 1
Decrement SP by 1
Decrement X by 1
Decrement Y by 1

M ← [M] − 1

A ← [A] − 1

B ← [B] − 1

SP ← [SP] − 1

X ← [X] − 1

Y ← [Y] − 1

Increment Instructions

Mnemonic Function Operation

inc <opr>
inca
incb
ins
inx
iny

Increment memory by 1
Increment A by 1
Increment B by 1
Increment SP by 1
Increment X by 1
Increment Y by 1

[M] + 1
A ← [A] + 1
B ← [B] + 1
SP ← [SP] + 1
X ← [X] + 1
Y ← [Y] + 1

M ←

Note: <opr> can be specified using direct, extended, or indexed addressing

modes.

Table 2.5 ■ Summary of decrement and increment instructions