
Addressing Modes 85
Data Register Direct
Address Register Direct
Address Register Indirect
Address Register Indirect with Postincrement
Address Register Indirect with Predecrement
Address Register Indirect with Displacement
Address Register Indirect with Index
Absolute Short
Absolute Long
Program Counter with Displacement
Program Counter with Index
Immediate
Exercises
1. Are source operands ever modified by an instruction?
2. What is an “effective address” ?
3. Is the 68000 a fully orthoganal machine?
4. What is the effective address for register direct mode?
5. Where is immediate data located?
6. What is the range of absolute short addressing?
7. What is a pointer?
8. How is address register indirect mode specified?
9. Use address register indirect mode to add the first 10 longwords
starting at absolute location $2000. Leave the result in DO.
10. Repeat the above problem using address register indirect with postin
crement addressing.
11. Write the instructions necessary to determine the length of a null
terminated string found at MYSTR. Leave the length value in register
DO.
12. With address register indirect with predecrementing or postincre
menting, is the value in the address register always modified by plus
or minus one?
13. What addressing modes are allowed with the CMPM instruction?
14. What is the range of the displacement for address register indirect
with displacement addressing?
15. Set up equates to define a record consisting of a 12-character (includ
ing the null) employee name, a longword employee number, and a
word salary.
16. For the above record definition, assume a pointer to the record is in
A4. Write the instruction that will place the salary data into DO.
Dn
An
(An)
(A n)+
“ (An)
d(An)
d(An, Ri)
xxx.W
xxx.L
d(PC)
d(PC, Ri)
#xxx
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