Lec5: instruction types

Lecture 5: instruction types Lecturer: Noor Kadhum

5.1 Instruction types
Operands specify the value an instruction is to operate on,
and where the result is to be stored. Instruction sets are
classified by the number of operands used. An instruction may
have no, one, two, or three operands.
1- Three addresses (operands)
In instruction that have three operands, one of the
operand specifies the destination as an address where the
result is to be saved. The other two operands specify the source
either as addresses of memory location or constants.

Example: Execute the following instruction using 3 address
format : x=c*b/r-d
Sol :
Step No. Step description 1 mul R1,c,b R1? c*b 2 sub R2,r,d R2 ? r-d 3 div x , R1,R2 X ? r1/r2
2- Two addresses
In this type both operands are sources. But the first
operand is used as destination therefore the first operand must
be an address in memory, but the second may be an address or
a constant.
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Babylon university - Sciences College For Women - Computer Dep. - Architecture For Third class