Page 47 - DCAP210_INTRODUCTION__TO_MICROPROCESSORS

Unit 3: Assembly Language Programming of 8085

Notes
Table 3.3: Opcode Operation

Opcode Operand Description
ADD R Add
(a) It ia a 1-byte instruction
(b) Adds the contents of register R to the contents of
Accumulator
ADI 8-bit Add Immediate
(a) It is a 2-byte instruction
(b) Adds the 8-bits (second byte) to the contents of the
Accumulator

SUB R Subtract
(a) It is a 1-byte instruction
(b) Subtracts the contents of register R from the contents
of the Accumulator
SUI 8-bit Subtract Immediate
(a) It is a 2-byte instruction
(b) Subtract the 8-bit (second byte) from the contents of
the Accumulator.

INR R Increment
(a) It is a 1-byte instruction
(b) Increases the contents of R by 1
DCR R Decrement
(a) It is a 1-byte instruction
(b) Decreases the contents of R by 1

9. The INR (increment) and DCR (decrement) uses only one of the registers. These do not affect
CY, even the result is larger than 8-bit.
3.3.3 Logical Operations

As 8085 microprocessor is a programmable logic chip, it can also perform hard-wired logic with
its instruction set. The logical operations performed by includes AND, OR, XOR (Exclusive OR)
and NOT (Complement). The logical instructions also assume that the Accumulator is one of the
operands and also the place where the result is stored. These operations also do not affect the
contents of source register. Except the CMA instruction, all other affect Z, P, and S flags according
to the result. The logic operations performed are listed in Table 3.4. These instructions perform
various logical operations with the contents of the accumulator.
AND, OR Exclusive OR: Any 8-bit number, or the contents of a register, or of a memory location
can be logically AND, O red, or Exclusive-O Red with the contents of the accumulator. The results
are stored in the accumulator.
Rotate: Each bit in the accumulator can be shifted either left or right to the next position.
Compare: Any 8-bit number or the contents of a register, or a memory location can be compared
for equality, greater than or less than, with the contents of the accumulator.
Complement: The contents of the accumulator can be complemented. All 0s are replaced by 1s
and all 1s are replaced by 0s.

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