HCS12 Assembly Programming - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 61

S

Figure 2.4 ■ An infinite loop

If there is concern that the relationship n 1 n 2 may not hold, then it must be checked at the

beginning of the loop. Four steps are required to implement a FOR loop.
Step 1
Initialize the loop counter and other variables.
Step 2
Compare the loop counter with the limit to see if it is within bounds. If it is, then perform
the specified operations. Otherwise, exit the loop.
Step 3
Increment (or decrement) the loop counter.
Step 4
Go to step 2.

≤

A For loop is illustrated in Figure 2.5.

W HILE C D O S
Whenever a While construct is executed, the logical expression C is evaluated first. If it
yields a false value, statement S will not be executed. The action of a While construct is illus-
trated in Figure 2.6. Four steps are required to implement a While loop.

i ← n 1 i ← n 2

No No

i ≤ n 2 ? ≥ n 1 ?

Yes Yes

S S

i ← i + 1 ← i - 1

(a) For i = n 1 to n 2 DO S (b) For i = n 2 down to n 1 DO S

Figure 2.5 ■ For looping construct