The document discusses the instruction formats and instruction set of the 8085 microprocessor. It describes the three main instruction formats as 1-byte, 2-byte, and 3-byte instructions. It then categorizes the instruction set into five groups - data transfer instructions, arithmetic instructions, logical instructions, branching instructions, and control instructions. For each group, it provides examples of common instructions and explains what operations they perform.

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Instruction Format
of 8085

2. Instruction format
Instruction format is defined as - Instruction is the command
given by the user to the microprocessor and need to be get
executed by the processor the entire group of instruction are
called instruction set and for properly working , these instruction
sets are arranged in a proper way which is known as instruction
format. .
Instruction format of 8085 has two fundamental fields.
(i) Opcode (information of operation)
(ii) Operand (address of location)
Type of instruction:- There are following three types of
instructions formats used in microprocessor -
(I) 1-byte instruction
(II) 2-byte instruction
(III) 3-byte instruction
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3. Classification of Instruction Set
• Data Transfer Instruction
• Arithmetic Instructions
• Logical Instructions
• Branching Instructions
• Control Instructions
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4. 1-byte instruction
A 1-byte instruction includes the opcode and a operand is
the same byte.
Example-1:
Task- Copy the contents of accumulator in register B.
Mnemonic- MOV B, A
Opcode- MOV
Operand- B, A
Hex Code- 47H
Binary code- 0100 0111
The length of these instructions is 8-bit; each requires one
memory location. The mnemonic is always followed by a
letter (or two letters) representing the registers (such as A,
B, C, D, E, H, L and SP).
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5. Two-byte instructions
Two-byte instruction is the type of instruction in which
the first 8 bits indicates the opcode and the next 8 bits
indicates the operand.
Example-1:
Task- Load the hexadecimal data 32H in the accumulator.
Mnemonic- MVI A, 32H
Opcode- MVI
Operand- A, 32H
Hex Code- 3E 32
Binary code- 0011 1110 0011 0010
Note – This type of instructions need two bytes to store
the binary codes. The mnemonic is always followed by 8-
bit (byte) data.
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6. 3- byte instruction
Three-byte instruction is the type of instruction in which the first 8 bits
indicates the opcode and the next two bytes specify the 16-bit
address. The low-order address is represented in second byte and the
high-order address is represented in the third byte.
Example-1:
Task- Load contents of memory 2050H in the accumulator.
Mnemonic- LDA 2050H
Opcode- LDA
Operand- 2050H
Hex Code- 3A
50
20
Binary code- 0011 1010
0101 0000
0010 0000
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7. Note – These instructions would require three
memory locations to store the binary codes. The
mnemonic is always followed by 16-bit
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9. Instruction Set of 8085 Microprocessor
An instruction is a binary command used to
execute an operation inside the microprocessor
over a given data.
A group of instructions that are supported by the
8085 microprocessor is known to be the instruction
set of 8085 microprocessor.
Basically, 8085 is designed to have 5 functional
categories of the instruction set.
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10. Instruction set of 8085 microprocessor
An instruction set is a group of instruction that
executes the desired operation on the data
specifically described by the microprocessor
8085.
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12. Data Transfer Instruction
• These instructions are used by the
microprocessor in order to transfer the data
from one location to another.
• More specifically, it helps in transferring the data
from source operand to destination operand,
without making any changes in the source data.
• As the data present in the source is not
modified. Thus it is more convenient to call it a
data copy instruction.
• As while transferring the data from source to
destination, the data present in the source is just
copied to the destination also. Due to this no
change in source data is noticed.
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13. Basically, the instructions that come under this
instruction set, are as follows:
This instruction helps to transfer the contents of
register r2 into register r1. While the data in register
r2 will remain the same.
This instruction transfers the data in register B to an
accumulator.
This instruction specifies the transfer of data present in
the memory to the register. However, the address of
the memory location must be present in the HL
register.
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14. Arithmetic Instruction
This instruction set allows arithmetic operations to be
performed over the data in memory and register inside the 8085
microprocessor.
This instruction specifies that the data present in the register is
to be added with the data present in the accumulator and the
result is to be stored in the accumulator itself.
This instruction is used to add the data of the memory address
specified at the operand with the data present at the
accumulator. And the result of the addition is stored in the
accumulator.
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15. Logical Instruction
These instructions are used to perform logical or Boolean
operations over the data present in either register or
memory. The logical instructions modify the flag bits
according to the operation performed.
This instruction is used to compare the data at the
accumulator with the data present at the register or
memory which is given as operand. According to the result
obtained by the comparison, the flags are set. While the
data being compared remains unchanged.
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16. Branching Instruction
These instructions are used in order to switch
or transfer the control of the microprocessor
from one position to another. More specifically
we can say, it changes the general sequential
flow.
The branching instruction set is given below:
This instruction is used to transfer the present
program sequence to that memory location
whose 16-bit address is specified in operand of
the instruction.
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17. Branching Instruction
These instructions are used in order to switch
or transfer the control of the microprocessor
from one position to another. More specifically
we can say, it changes the general sequential
flow.
The branching instruction set is given below:
This instruction is used to transfer the present
program sequence to that memory location
whose 16-bit address is specified in operand of
the instruction.
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18. Control Instruction
As the name itself is suggesting that these
instructions are used to control the operations
of the microprocessor. The control instructions
are as follows
It stands for no operation. Whenever the
microprocessor fetches this instruction, then it
is decoded but not executed.
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19. Control Instruction
It is used to disable the interrupts generated in the
microprocessor. Resetting of interrupt enable flip-flop
is performed. This leads to disabling of all the
interrupts except TR
AP.
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