Motorola M68000 Uživatelská příručka stáhnout pdf (Strana 82)

68 Assembly Language Programming for the 68000 Family

Exercises

Assume longword operands unless otherwise specified.

1. What CCR bit is used to detect overflow of unsigned arithmetic

operations?

2. What CCR bit is used to detect overflow of signed arithmetic opera

tions?

3. Is there a limit as to how far away the label of a conditional branch

may be?

4. What CCR bit determines if the result of an arithmetic operation is

zero?

5. What CCR bit determines if the result of an arithmetic operation is

positive or negative?

6. What is the difference between the CMP instruction and the SUB

instruction?

7. Write the instructions necessary to branch to label STOP if the DO

8. Write the instructions to branch to label BIGER if register DO is larger

than variable LIMIT. Assume unsigned values.

9. What CCR bits were discussed in this chapter?

10. Are all the bits of the CCR used?

11. If we add the following unsigned bytes, will the carry bit be set? The

values are in decimal.

55 and 27

150 and 110

12. If we add the following signed bytes, will the overflow bit be set?

The values are in decimal.

—100 and +50

—100 and —50

13. Write the instructions necessary to add the signed values in the DO

and D1 register and branch to label OK if there is no overflow.

14. Repeat the above problem for unsigned values.

15. Write the instructions necessary to test if register DO is zero and, if

so, to branch to label ZERO.

16. Write the instructions necessary to compare variables NUM1 and

NUM2, branching to label EQUAL if they are equal, to label LESS

if NUM1 is less than NUM2. Assume signed values.

17. Write the equivalent of the DBRA instruction using instructions intro

duced in this chapter.

18. What is the purpose of the extend bit?

19. What is the advantage of using ADDQ and SUBQ rather than ADD

AND SUB?

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